Biology Commons^™

The Distribution Of Lianas And Their Change In Abundance In Temperate Forests Over The Past 45 Years, Ronald A. Londre, Stefan A. Schnitzer

Biological Sciences Faculty Research and Publications

Lianas (woody vines) are an important and dynamic component of many forests throughout the world, and increases in CO₂, mean winter temperature, and forest fragmentation may promote their growth and proliferation in temperate forests. In this study, we used a 45‐year data set to test the hypothesis that lianas have increased in abundance and basal area in the interiors of 14 deciduous temperate forests in Wisconsin (USA) since 1959. We also censused woody plants along a gradient from the forest edge to the interior in seven of these forests to test the hypothesis that the abundance of lianas …

Adherens Junction-Associated Protein Distribution Differs In Smooth Muscle Tissue And Acutely Isolated Cells, Thomas J. Eddinger, Jessen D. Schiebout, Darl R. Swartz

Biological Sciences Faculty Research and Publications

This study was designed to examine how smooth muscle (SM) cell (SMC) isolation affects the distribution of some adherens junction (AJ) complex-associated proteins. Immunofluorescence procedures for identifying protein distribution were used on gastrointestinal and tracheal SM tissues and freshly isolated SMCs from dogs and rabbits. As confirmed by force measurements, relaxation, Ca²⁺ depletion, and cholinergic activation of SM tissues do not cause significant redistribution of the AJ-associated proteins vinculin, talin, or fibronectin away from the plasma membrane. Unlike SMCs in tissue, freshly isolated SMCs show a variable peripheral/ cytoplasmic vinculin and talin distribution that is not altered by activation. …

Spinobulbar Neurons In Lamprey: Cellular Properties And Synaptic Interactions, James F. Einum, James T. Buchanan

Biological Sciences Faculty Research and Publications

An in vitro preparation of the nervous system of the lamprey, a lower vertebrate, was used to characterize the properties of spinal neurons with axons projecting to the brain stem [i.e., spinobulbar (SB) neurons)]. To identify SB neurons, extracellular electrodes on each side of the spinal cord near the obex recorded the axonal spikes of neurons impaled with sharp intracellular microelectrodes in the rostral spinal cord. The ascending spinal neurons (n = 144) included those with ipsilateral (iSB) (63/144), contralateral (cSB) (77/144), or bilateral (bSB) (4/144) axonal projections to the brain stem. Intracellular injection of biocytin revealed that the …

Resistance To Pressure-Induced Dilatation In Femoral But Not Saphenous Artery: Physiological Role Of Latch?, Christopher Call, Shaojie Han, John E. Speich, Thomas J. Eddinger, Paul H. Ratz

Biological Sciences Faculty Research and Publications

We recently determined that the ability of the femoral artery (FA) to maintain higher levels of tonic isometric stress compared with the saphenous artery (SA) was due to differential expression of motor proteins permitting latch-bridge formation in FA and not SA. Arteries under pressure in vivo are not constrained to contract isometrically. Thus the significance of latch-bridge formation in arterial physiology remains to be determined. To address this translational question, diameter changes of pressurized FA and SA were compared. The reduction in lumen diameter induced by KCl at 80 mmHg (isobaric active constriction; IAC) was greater at 30 s than …

Low Cell Ph Depresses Peak Power In Rat Skeletal Muscle Fibres At Both 30°C And 15°C: Implications For Muscle Fatigue, Shannon T. Knuth, H. L. W. Dave, Jim R. Peters, Robert H. Fitts

Biological Sciences Faculty Research and Publications

Historically, an increase in intracellular H⁺ (decrease in cell pH) was thought to contribute to muscle fatigue by direct inhibition of the cross-bridge leading to a reduction in velocity and force. More recently, due to the observation that the effects were less at temperatures closer to those observed in vivo, the importance of H⁺ as a fatigue agent has been questioned. The purpose of this work was to re-evaluate the role of H⁺ in muscle fatigue by studying the effect of low pH (6.2) on force, velocity and peak power in rat fast-and slow-twitch muscle fibres …

Characterization Of Mmp37p, A Saccharomyces Cerevisiae Mitochondrial Matrix Protein With A Role In Mitochondrial Protein Import, Michelle R. Gallas, Mary Kathryn Dienhart, Rosemary A. Stuart, Roy M. Long

Biological Sciences Faculty Research and Publications

Many mitochondrial proteins are encoded by nuclear genes and after translation in the cytoplasm are imported via translocases in the outer and inner membranes, the TOM and TIM complexes, respectively. Here, we report the characterization of the mitochondrial protein, Mmp37p (YGR046w) and demonstrate its involvement in the process of protein import into mitochondria. Haploid cells deleted of MMP37 are viable but display a temperature-sensitive growth phenotype and are inviable in the absence of mitochondrial DNA. Mmp37p is located in the mitochondrial matrix where it is peripherally associated with the inner membrane. We show that Mmp37p has a role in the …

Censusing And Measuring Lianas: A Quantitative Comparison Of The Common Methods, Stefan A. Schnitzer, Saara J. Dewalt, Jérôme Chave

Biological Sciences Faculty Research and Publications

Lianas contribute to many aspects of tropical forest diversity and dynamics, and interest in liana ecology has grown substantially in recent years. Methods to census lianas and estimate biomass, however, differ among studies, possibly hindering attempts to compare liana communities. At Nouragues Research Station (French Guiana), we tested the extent to which liana abundance, basal area, and estimated biomass differed depending on stem diameter measurement location, inclusion of ramets, inclusion of lianas rooted within versus passing through the plot, and plot shape. We found that the mean per plot abundance and basal area of lianas were significantly greater when lianas …

Macronuclear Genome Sequence Of The Ciliate Tetrahymena Thermophila, A Model Eukaryote, Jonathan A. Eisen, Robert S. Coyne, Martin Wu, Dongying Wu, Mathangi Thiagarajan, Jennifer R. Wortman, Jonathan H. Badger, Qinghu Ren, Paolo Amedeo, Kristie M. Jones, Luke J. Tallon, Arthur L. Delcher, Steven L. Salzberg, Joana C. Silva, Brian J. Haas, William H. Majoros, Maryam Farzad, Jane M. Carlton, Roger K. Smith, Jyoti Garg, Ronald E. Pearlman, Kathleen M. Karrer, Lei Sun, Gerard Manning, Nels C. Elde, Aaron P. Turkewitz, David J. Asai, David E. Wilkes, Yufeng Wang, Hong Cai, Kathleen Collins, B. Andrew Stewart, Suzanne R. Lee, Katarzyna Wilamowska, Zasha Weinberg, Walter L. Ruzzo, Dorota Wloga, Jacek Gaertig, Joseph Frankel, Che-Chia Tsao, Martin A. Gorovsky, Patrick J. Keeling, Ross F. Waller, Nicola J. Patron, J. Michael Cherry, Nicholas A. Stover, Cynthia J. Krieger, Christina Del Toro, Hilary F. Ryder, Sondra C. Williamson, Rebecca A. Barbeau, Eileen P. Hamilton, Eduardo Orias

Biological Sciences Faculty Research and Publications

The ciliate Tetrahymena thermophila is a model organism for molecular and cellular biology. Like other ciliates, this species has separate germline and soma functions that are embodied by distinct nuclei within a single cell. The germline-like micronucleus (MIC) has its genome held in reserve for sexual reproduction. The soma-like macronucleus (MAC), which possesses a genome processed from that of the MIC, is the center of gene expression and does not directly contribute DNA to sexual progeny. We report here the shotgun sequencing, assembly, and analysis of the MAC genome of T. thermophila, which is approximately 104 Mb in length and …

Progeny Of Germ Line Knockouts Of Asi2, A Gene Encoding A Putative Signal Transduction Receptor In Tetrahymena Thermophila, Fail To Make The Transition From Sexual Reproduction To Vegetative Growth, Shuqiang Li, Lihui Yin, Eric S. Cole, Rupa A. Udani, Kathleen M. Karrer

Biological Sciences Faculty Research and Publications

The ciliated protozoan Tetrahymena has two nuclei: a germ line micronucleus and a somatic macronucleus. The transcriptionally active macronucleus has about 50 copies of each chromosome. At sexual reproduction (conjugation), the parental macronucleus is degraded and new macronucleus develops from a mitotic product of the zygotic micronucleus. Development of the macronucleus involves massive genome remodeling, including deletion of about 6000 specific internal eliminated sequences (IES) and multiple rounds of DNA replication. A gene encoding a putative signal transduction receptor, ASI2, (anlagen stage induced 2) is up-regulated during development of the new macronuclei (anlagen). Macronuclear ASI2 is nonessential for vegetative …

Evidence For Absence Of Latch-Bridge Formation In Muscular Saphenous Arteries, Shaojie Han, John E. Speich, Thomas J. Eddinger, Krystina M. Berg, Amy S. Miner, Chris Call, Paul H. Ratz

Biological Sciences Faculty Research and Publications

Large-diameter elastic arteries can produce strong contractions indefinitely at a high-energy economy by the formation of latch bridges. Whether ownstream blood vessels also use latch bridges remains unknown. The zero-pressure medial thickness and lumen diameter of rabbit saphenous artery (SA), a muscular branch of the elastic femoral artery (FA), were, respectively, approximately twofold and half-fold that of the FA. In isolated FA and SA rings, KCl rapidly (s) caused strong increases in isometric stress (1.2 x 10⁵ N/m²) and intracellular Ca²⁺ concentration ([Ca²⁺]_i; 250 nM). By 10 min, [Ca²⁺]i declined …

Tumor Suppressor Activity Of Odc Antizyme In Mek-Driven Skin Tumorigenesis, David J. Feith, Sofia Origanti, Paula L. Shoop, Suzanne Sass-Kuhn, Lisa M. Shantz

Biological Sciences Faculty Research and Publications

To test the hypothesis that suppression of ornithine decarboxylase (ODC) activity blocks the promotion of target cells in the outer root sheath of the hair follicle initiated by Raf/MEK/ERK activation, we crossed mice overexpressing an activated MEK mutant in the skin (K14-MEK mice) with two transgenic lines overexpressing antizyme (AZ), which binds to ODC and targets it for degradation. K14-MEK mice develop spontaneous skin tumors without initiation or promotion. These mice on the ICR background were crossed with K5-AZ and K6-AZ mice on both the carcinogenesis-resistant C57BL/6 background and the sensitive DBA/2 background. Expression of AZ driven by either the …

Ampk Regulation Of Mouse Oocyte Meiotic Resumption In Vitro, Jing Chen, Emma R. Hudson, Maggie M. Chi, Aimee S. Chang, Kelle H. Moley, D. Grahame Hardie, Stephen M. Downs

Biological Sciences Faculty Research and Publications

We have previously shown that the adenosine analog 5-aminoimidazole-4-carboxamide-1-β-d-ribofuranoside (AICAR), an activator of AMP-activated protein kinase (AMPK), stimulates an increase in AMPK activity and induces meiotic resumption in mouse oocytes [Downs, S.M., Hudson, E.R., Hardie, D.G., 2002. A potential role for AMP-activated protein kinase in meiotic induction in mouse oocytes. Dev. Biol, 245, 200–212]. The present study was carried out to better define a causative role for AMPK in oocyte meiotic maturation. When microinjected with a constitutively active AMPK, about 20% of mouse oocytes maintained in meiotic arrest with dibutyryl cAMP (dbcAMP) were stimulated to undergo germinal vesicle breakdown (GVB), …

Cardiorespiratory Responses To Physical Work During And Following 17 Days Of Bed Rest And Spaceflight, Todd A. Trappe, Scott Trappe, Gary A. Lee, Jeffrey J. Widrick, Robert H. Fitts, David Costill

Biological Sciences Faculty Research and Publications

To determine the influence of a 17-day exposure to real and simulated spaceflight (SF) on cardiorespiratory function during exercise, four male crewmembers of the STS-78 space shuttle flight and eight male volunteers were studied before, during, and after the 17-day mission and 17 days of -6° head-down-tilt bed rest (BR), respectively. Measurements of oxygen uptake, pulmonary ventilation, and heart rate were made during submaximal cycling 60, 30, and 15 days before the SF liftoff and 12 and 7 days before BR; on SF days 2, 8, and 13 and on BR days 2, 8, and 13; and on days …

Nuclear Rna Surveillance In Saccharomyces Cerevisiae: Trf4p-Dependent Polyadenylation Of Nascent Hypomethylated Trna And An Aberrant Form Of 5s Rrna, Sujatha A. Kadaba, Xuying Wang, James T. Anderson

Biological Sciences Faculty Research and Publications

1-Methyladenosine modification at position 58 of tRNA is catalyzed by a two-subunit methyltransferase composed of Trm6p and Trm61p in Saccharomyces cerevisiae. Initiator tRNA (tRNA_i^Met) lacking m¹A58 (hypomethylated) is rendered unstable through the cooperative function of the poly(A) polymerases, Trf4p/Trf5p, and the nuclear exosome. We provide evidence that a catalytically active Trf4p poly(A) polymerase is required for polyadenylation of hypomethylated tRNA_i^Met in vivo. DNA sequence analysis of tRNA_i^Met cDNAs and Northern hybridizations of poly(A)+ RNA provide evidence that nascent pre-tRNA_i^Met transcripts are targeted for polyadenylation and degradation. We determined …

Radial Spoke Proteins Of Chlamydomonas Flagella, Pinfen Yang, Dennis R. Diener, Chun Yang, Takahiro Kohno, Gregory J. Pazour, Jennifer M. Dienes, Nathan S. Agrin, Stephen M. King, Winfield S. Sale, Ritsu Kamiya, Joel L. Rosenbaum, George B. Witman

Biological Sciences Faculty Research and Publications

The radial spoke is a ubiquitous component of `9+2' cilia and flagella, and plays an essential role in the control of dynein arm activity by relaying signals from the central pair of microtubules to the arms. The Chlamydomonas reinhardtii radial spoke contains at least 23 proteins, only 8 of which have been characterized at the molecular level. Here, we use mass spectrometry to identify 10 additional radial spoke proteins. Many of the newly identified proteins in the spoke stalk are predicted to contain domains associated with signal transduction, including Ca²⁺-, AKAP- and nucleotide-binding domains. This suggests that the …

Predicting Liana Crown Location From Stem Diameter In Three Panamanian Lowland Forests, Brian P. Kurzel, Stefan A. Schnitzer, Walter P. Carson

Biological Sciences Faculty Research and Publications

In three forests that differed in annual rainfall and seasonality, the probability of a liana with a stem ≥2.0 cm stem diameter reaching the canopy was >50 percent. Lianas reached the canopy at significantly smaller size‐classes (1.5 cm) in the wet aseasonal forest, suggesting that this estimate changes with forest type. Nevertheless, as a general rule, we suggest that 2.0 cm is the minium stem diameter to examine the abundance and diversity of canopy lianas or canopy competition between lianas and trees.

A Standard Protocol For Liana Censuses, Jeffrey J. Gerwing, Stefan A. Schnitzer, Robyn J. Burnham, Frans Bongers, Jérôme Chave, Saara J. Dewalt, Corneille E.N. Ewango, Robin Foster, David Kenfack, Miguel Martinez-Ramos, Marc P.E. Parren, Narayanaswamy Parthasarathy, Diego R. Perez-Salicrup, Francis E. Putz, Duncan W. Thomas

Biological Sciences Faculty Research and Publications

A recent increase in published studies of lianas has been paralleled by a proliferation of protocols for censusing lianas. This article seeks to increase uniformity in liana inventories by providing specific recommendations for the determination of which taxa to include, the location of diameter measurement points on individual stems, the setting of minimum stem diameter cutoffs, the treatment of multiple‐stemmed and rooted clonal groups, and the measurement of noncylindrical stems. Use of more uniform liana censusing protocols may facilitate comparison of independently collected data sets and further our understanding of global patterns in liana abundance, diversity, biomass, and dynamics.

Contribution Of Msh2 And Msh6 Subunits To The Asymmetric Atpase And Dna Mismatch Binding Activities Of Saccharomyces Cerevisiae Msh2–Msh6 Mismatch Repair Protein, Edwin Antony, Sapna Khubchandani, Siying Chen, Manju M. Hingorani

Biological Sciences Faculty Research and Publications

Previous analyses of both Thermus aquaticus MutS homodimer and Saccharomyces cerevisiae Msh2–Msh6 heterodimer have revealed that the subunits in these protein complexes bind and hydrolyze ATP asymmetrically, emulating their asymmetric DNA binding properties. In the MutS homodimer, one subunit (S₁) binds ATP with high affinity and hydrolyzes it rapidly, while the other subunit (S₂) binds ATP with lower affinity and hydrolyzes it at an apparently slower rate. Interaction of MutS with mismatched DNA results in suppression of ATP hydrolysis at S₁—but which of these subunits, S₁ or S₂, makes specific contact …

The Flagellar Motility Of Chlamydomonas Pf25 Mutant Lacking An Akap-Binding Protein Is Overtly Sensitive To Medium Conditions, Chun Yang, Pinfen Yang

Biological Sciences Faculty Research and Publications

Radial spokes are a conserved axonemal structural complex postulated to regulate the motility of 9 + 2 cilia and flagella via a network of phosphoenzymes and regulatory proteins. Consistently, a Chlamydomonas radial spoke protein, RSP3, has been identified by RII overlays as an A-kinase anchoring protein (AKAP) that localizes the cAMP-dependent protein kinase (PKA) holoenzyme by binding to the RIIa domain of PKA RII subunit. However, the highly conserved docking domain of PKA is also found in the N termini of several AKAP-binding proteins unrelated to PKA as well as a 24-kDa novel spoke protein, RSP11. Here, we report that …

An Engineered Nonsense Ura3 Allele Provides A Versatile System To Detect The Presence, Absence And Appearance Of The [Em>Psi+] Prion In Saccharomyces Cerevisiae, Anita L. Manogaran, Kathryn T. Kirkland, Susan W. Liebman

Biological Sciences Faculty Research and Publications

Common methods to identify yeast cells containing the prion form of the Sup35 translation termination factor, [PSI⁺], involve a nonsense suppressor phenotype. Decreased function of Sup35p in [PSI⁺] cells leads to readthrough of certain nonsense mutations in a few auxotrophic markers, for example, ade1-14. This readthrough results in growth on adenine deficient media. While this powerful tool has dramatically facilitated the study of [PSI⁺], it is limited to a narrow range of laboratory strains and cannot easily be used to screen for cells that have lost the [PSI^{+ …}

Smooth Muscle Adherens Junctions Associated Proteins Are Stable At The Cell Periphery During Relaxation And Activation, Thomas J. Eddinger, Jessen D. Schiebout, Darl R. Swartz

Biological Sciences Faculty Research and Publications

This study was performed to determine the stability of the adherens junction (AJ)-associated proteins at the smooth muscle cell (SMC) plasma membrane during relaxing and activating conditions. Dog stomach, ileum, colon, and trachea tissues were stored in Ca²⁺-free PSS or regular PSS or were activated in 10 μM carbachol in PSS before rapid freezing. The tissues were subsequently sectioned and immunoreacted using antibodies for vinculin, talin, fibronectin, and caveolin to determine their cellular distribution in these tissues under these conditions. In all four tissues and under all three conditions, the distribution of these four proteins remained localized to …

Disentangling Above‐ And Below‐Ground Competition Between Lianas And Trees In A Tropical Forest, Stefan A. Schnitzer, Mirjam E. Kuzee, Frans Bongers

Biological Sciences Faculty Research and Publications

1. Light is thought to be the most limiting resource in tropical forests, and thus above‐ground competition is commonly accepted as the mechanism that structures these communities. In many tropical forests, trees compete not only with other trees, but also with lianas, which compete aggressively for below‐ground resources and thus may limit tree growth and regeneration.
2. Using a replicated experiment, we tested the relative strengths of above‐ and below‐ground competition from lianas on tree saplings in a disturbed forest in Côte d’Ivoire with a heterogeneous canopy and relatively high light penetration. We planted seedlings of three tree species and subjected them …

The Depressive Effect Of PI On The Force-Pca Relationship In Skinned Single Muscle Fibers Is Temperature Dependent, Edward Patrick Debold, Janell Romatowski, Robert H. Fitts

Biological Sciences Faculty Research and Publications

Increases in P_i combined with decreases in myoplasmic Ca2+ are believed to cause a significant portion of the decrease in muscular force during fatigue. To investigate this further, we determined the effect of 30 mM P_ion the force-Ca²⁺ relationship of chemically skinned single muscle fibers at near-physiological temperature (30°C). Fibers isolated from rat soleus (slow) and gastrocnemius (fast) muscle were subjected to a series of solutions with an increasing free Ca²⁺ concentration in the presence and absence of 30 mM P_iat both low (15°C) and high (30°C) temperature. In slow fibers, 30 mM …

Modulation Of Tyramine Signaling By Osmolality In An Insect Secretory Epithelium, Edward M. Blumenthal

Biological Sciences Faculty Research and Publications

The control of water balance in multicellular organisms depends on absorptive and secretory processes across epithelia. This study concerns the effects of osmolality on the function of the Malpighian tubules (MTs), a major component of the insect excretory system. Previous work has shown that the biogenic amine tyramine increases transepithelial chloride conductance and urine secretion in Drosophila MTs. This study demonstrates that the response of MTs to tyramine, as measured by the depolarization of the transepithelial potential (TEP), is modulated by the osmolality of the surrounding medium. An increase in osmolality caused decreased tyramine sensitivity, whereas a decrease in osmolality …

The Let-7 Microrna Family Members Mir-48, Mir-84, And Mir-241 Function Together To Regulate Developmental Timing In Caenorhabditis Elegans, Allison L. Abbott, Ezequiel Alvarez-Saavedra, Eric A. Miska, Nelson C. Lau, David P. Bartel, H. Robert Horvitz, Victor R. Ambros

Biological Sciences Faculty Research and Publications

The microRNA let-7 is a critical regulator of developmental timing events at the larval-to-adult transition in C. elegans. Recently, microRNAs with sequence similarity to let-7 have been identified. We find that doubly mutant animals lacking the let-7 family microRNA genes mir-48 and mir-84 exhibit retarded molting behavior and retarded adult gene expression in the hypodermis. Triply mutant animals lacking mir-48, mir-84, and mir-241 exhibit repetition of L2-stage events in addition to retarded adult-stage events. mir-48, mir-84, and mir-241 function together to control the L2-to-L3 transition, likely by base pairing to complementary sites in the …

Rna Turnover: Unexpected Consequences Of Being Tailed, James T. Anderson

Biological Sciences Faculty Research and Publications

In eukaryotic cells, the 3′ poly(A) tails found on mRNA influence their stability and translation. The discovery of a second nuclear poly(A) polymerase complex has fueled a series of reports defining a new and unexpected role for 3′ end poly(A) tails in the nuclear surveillance and turnover of noncoding RNAs and intergenic mRNAs of unknown function.

A Mechanistic Explanation For Global Patterns Of Liana Abundance And Distribution, Stefan A. Schnitzer

Biological Sciences Faculty Research and Publications

One of the main goals in ecology is determining the mechanisms that control the abundance and distribution of organisms. Using data from 69 tropical forests worldwide, I demonstrate that liana (woody vine) abundance is correlated negatively with mean annual precipitation and positively with seasonality, a pattern precisely the opposite of most other plant types. I propose a general mechanistic hypothesis integrating both ecological and ecophysiological approaches to explain this pattern. Specifically, the deep root and efficient vascular systems of lianas enable them to suffer less water stress during seasonal droughts while many competitors are dormant, giving lianas a competitive advantage …

Membrane Potential Oscillations In Reticulospinal And Spinobulbar Neurons During Locomotor Activity, James F. Einum, James T. Buchanan

Biological Sciences Faculty Research and Publications

Feedback from the spinal locomotor networks provides rhythmic modulation of the membrane potential of reticulospinal (RS) neurons during locomotor activity. To further understand the origins of this rhythmic activity, the timings of the oscillations in spinobulbar (SB) neurons of the spinal cord and in RS neurons of the posterior and middle rhombencephalic reticular nuclei were measured using intracellular microelectrode recordings in the isolated brain stem-spinal cord preparation of the lamprey. A diffusion barrier constructed just caudal to the obex allowed induction of locomotor activity in the spinal cord by bath application of an excitatory amino acid to the spinal bath. …

Water Uptake And Transport In Lianas And Co-Occurring Trees Of A Seasonally Dry Tropical Forest, Jose Luis Andrade, Frederick C. Meinzer, Stefan A. Schnitzer

Biological Sciences Faculty Research and Publications

Water uptake and transport were studied in eight liana species in a seasonally dry tropical forest on Barro Colorado Island, Panama. Stable hydrogen isotope composition (δD) of xylem and soil water, soil volumetric water content (θ_v), and basal sap flow were measured during the 1997 and 1998 dry seasons. Sap flow of several neighboring trees was measured to assess differences between lianas and trees in magnitudes and patterns of daily sap flow. Little seasonal change in θ_v was observed at 90–120 cm depth in both years. Mean soil water δD during the dry season was −19‰ at …

Role Of A Conserved Glutamate Residue In The Escherichia Coli Seca Atpase Mechanism, Christopher R. Zito, Edwin Antony, John F. Hunt, Donald B. Oliver, Manju M. Hingorani

Biological Sciences Faculty Research and Publications

Escherichia coli SecA uses ATP to drive the transport of proteins across cell membranes. Glutamate 210 in the “DEVD” Walker B motif of the SecA ATP-binding site has been proposed as the catalytic base for ATP hydrolysis (Hunt, J. F., Weinkauf, S., Henry, L., Fak, J. J., McNicholas, P., Oliver, D. B., and Deisenhofer, J. (2002) Science 297, 2018–2026). Consistent with this hypothesis, we find that mutation of glutamate 210 to aspartate results in a 90-fold reduction of the ATP hydrolysis rate compared with wild type SecA, 0.3 s^–1versus 27 s^–1, respectively. SecA-E210D also releases ADP …