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Query: UMLS:C0009443 (cold)
 92,137 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

A substitution mutation of Pro17 by Val (P17V) was constructed in the guanine nucleotide binding domain of Era, an essential protein in Escherichia coli. The mutation is analogous to the oncogenic activating allele at position 12 in the GTP-binding domain of p21ras. The phenotype of this mutant was analysed in a strain which exclusively expressed the mutant protein (Era-V17) in null allele chromosomal background (era1: :kan). The strain was found to be cold-sensitive for growth. Mutant Era-V17 purified from the strain was cold-sensitive for GTP-hydrolytic activity, suggesting that the GTPase activity of Era is required for cell growth since the P17V mutation resulted in both cold-sensitive growth of cells and cold-labile GTPase activity of the purified protein.
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PMID:Cold-sensitive growth and decreased GTP-hydrolytic activity from substitution of Pro17 for Val in Era, an essential Escherichia coli GTPase. 152 46

It has been found that preparations of Escherichia coli (MRE-600) ribosomes can display GTPase and ATPase activities independent of elongation factors EF-Tu and EF-G. The GTPase and ATPase are localized on ribosomal 50S subparticles, whereas 30S subparticles are free of the activities and do not stimulate them upon association with the 50S subparticles to form complete ribosomes. The GTPase and ATPase can be removed from the ribosomes and their 50S subparticles by treatment with 1 M NH4Cl or 50% ethanol in the cold. Ribosomal preparations freed from the factor-independent GTPase and ATPase retain their basic functional features. The data obtained do not permit to solve finally whether the factor-independent GTPase and ATPase revealed are components of ribosomes or represent a contamination rather firmly bound to the ribosomes. However, in any case this finding can contribute to an uncoupled hydrolysis of GTP and should be considered when studying the stoichiometry of triphosphate expenditure in the process of ribosomal protein synthesis.
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PMID:[Stoichiometry of GTP hydrolysis during peptide synthesis on the ribosome. I. Factor-independent GTPase and ATPase of ribosomal preparations]. 611 12

Our experiments have delineated the flow of information in the cyclic nucleotide cascade of vision of ROS. A single, photoexcited rhodopsin molecule activates several hundred phosphodiesterase molecules in two stages. First, photoexcited rhodopsin (R*) interacts with transducin (T), a peripheral membrane protein consisting of alpha- (39 kD), beta- (36 kD), and gamma- (approximately 10 kD) subunits. R* catalyzes the exchange of GTP for GDP bound to the subunit of transducin. About 500 T alpha- GTPs are produced per photoexcited rhodopsin at low light levels. T alpha-GTP, released from the beta- and gamma-subunits of transducin, then interacts with the phosphodiesterase to relieve the inhibitory constraint imposed by its gamma-subunit. Hydrolysis of GTP bound to T alpha serves to restore the system to the dark state. Transducin is the amplified signal carrier in this light-triggered cascade. The formation of hundreds of T alpha- GTPs is likely to be the first stage of amplification in visual excitation. The photoactivation of the phosphodiesterase in ROS closely resembles the activation of adenylate cyclase in hormone-sensitive cells. Our cholera toxin labeling studies have shown that transducin is akin to the signal-coupling G protein of the adenylate cyclase system. Cholera toxin specifically ADP- ribosylates and inactivates the GTPase activity of T alpha, just as it does with Gs. The action of pertussis toxin on ROS further underscores the homology of the photoreceptor and hormone-responsive systems. It seems likely that transducin, the stimulatory G protein, and the inhibitory G protein are members of the same family of signal-amplifying proteins. The study of the cyclic nucleotide cascade of vision is proving to be rewarding in affording a view of a recurring motif of signal amplification in nature in addition to providing insight into the mechanism of vision.
Cold Spring Harb Symp Quant Biol 1983
PMID:Transducin and the cyclic GMP phosphodiesterase: amplifier proteins in vision. 632 79

Treatment of isolated factor F1 by 1% dimethylsuberimidate in the presence of 50 mM (NH4)2SO4 leads to the formation of four different types of cross-linked dimers of the subunits, on average one dimer per molecule of the enzyme. This treatment results in 60-70% inactivation of factor F1. Factor F1 treated with dimethylsuberimidate does not show a change in the sedimentation coefficient and is not inactivated in the cold; it is not inactivated in the presence of Mg2+ either, nor is it activated by anions. Incubation of the cross-linked factor F1 with ADP does not lead to inactivation, although the ability to tightly bind ADP is retained. The total quantity of tightly bound ADP reaches 5 mol per mol of the cross-linked factor F1. Cross-linking of factor F1 also prevents the slow inactivation of the enzyme coupled with the hydrolysis of Mg-ATP and Mg-GTP. The dependence of the inactivation rate constant on the concentration of Mg-ATP and Mg-GTP at substrate concentrations of 0.05-2 mM is characterized by the same values of Km,app as those of the ATPase and GTPase activities of factor F1. The probability of the inactivation of factor F1 per turnover remains constant for all the concentrations of the substrates studied and is 2 . 10(-6) per turnover for the ATPase reaction and 2 . 10(-5) per turnover for the GTPase reaction. Moderate hydrostatic pressure (up to 150 atmospheres) greatly accelerates ATP-induced inactivation of factor F1. The activation volume (delta V*) of the inactivation process is equal to 5.1 . 10(-4) cm3/g, which is evidence of considerable changes in the extent of protein hydration during inactivation. Inactivation of the enzyme under pressure is accompanied by dissociation into subunits. Dimethyladipimidate, which does not cause intersubunit cross-linking in the molecule of factor F1, does not alter the properties of the native enzyme. It is suggested that the formation of one intersubunit cross-link in the molecule of factor F1 by dimethylsuberimidate affects the ability of the enzyme to undergo co-operative rearrangements of the quaternary structure under the influence of Mg2+, ADP, ATP, anions, and low temperature. The rate constants of ATP binding to the active site of factor F2 (k+1) = 2 . 10(8) M-1 . min-1), of ATP release from the active site (k-1 = 2 . 10(-2) min-1), and of ADP and Pi release from the active site (k2 = 5 . 10(3) min-1) have been determined. The results obtained confirm the correctness of Boyer's idea, according to which ATP is formed in the active site of mitochondrial ATPase without any external source of energy. Energy is used at the stage of the release of synthesized ATP from the active site of ATPase in the solution.
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PMID:Structural rearrangements in soluble mitochondrial ATPase. 645 13

Conditional cold-sensitive mutations in Era, an essential Escherichia coli GTPase, were isolated. Localized random polymerase chain reaction (PCR) mutagenesis employing Taq and T7 DNA polymerases under error prone amplification conditions was exploited to generate mutations in the era gene. A plasmid exchange technique was used to identify conditional cold-sensitive mutations in Era that give rise to defective cell growth below 30 degrees C. Three recessive missense mutations in Era, N26S, A156D, and E200K, were isolated. All three mutations are located at residues conserved in Era homologues from Streptococcus mutans and Coxiella burnetti.
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PMID:Cold-sensitive conditional mutations in Era, an essential Escherichia coli GTPase, isolated by localized random polymerase chain reaction mutagenesis. 772 73

The IPL2 gene is known to be required for normal polarized cell growth in the budding yeast Saccharomyces cerevisiae. We now show that IPL2 is identical to the previously identified BEM2 gene. bem2 mutants are defective in bud site selection at 26 degrees C and localized cell surface growth and organization of the actin cytoskeleton at 37 degrees C. BEM2 encodes a protein with a COOH-terminal domain homologous to sequences found in several GTPase-activating proteins, including human Bcr. The GTPase-activating protein-domain from the Bem2 protein (Bem2p) or human Bcr can functionally substitute for Bem2p. The Rho1 and Rho2 GTPases are the likely in vivo targets of Bem2p because bem2 mutant phenotypes can be partially suppressed by increasing the gene dosage of RHO1 or RHO2. CDC55 encodes the putative regulatory B subunit of protein phosphatase 2A, and mutations in BEM2 have previously been identified as suppressors of the cdc55-1 mutation. We show here that mutations in the previously identified GRR1 gene can suppress bem2 mutations. grr1 and cdc55 mutants are both elongated in shape and cold-sensitive for growth, and cells lacking both GRR1 and CDC55 exhibit a synthetic lethal phenotype. bem2 mutant phenotypes also can be suppressed by the SSD1-vl (also known as SRK1) mutation, which was shown previously to suppress mutations in the protein phosphatase-encoding SIT4 gene. Cells lacking both BEM2 and SIT4 exhibit a synthetic lethal phenotype even in the presence of the SSD1-v1 suppressor. These genetic interactions together suggest that protein phosphorylation and dephosphorylation play an important role in the BEM2-mediated process of polarized cell growth.
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PMID:Control of cellular morphogenesis by the Ip12/Bem2 GTPase-activating protein: possible role of protein phosphorylation. 796 97

Microtubule assembly was examined in the high-speed supernatant from homogenates of young (2-4 months old) and old (more than 24 months old) rat brains and significant age-related differences in microtubule assembly were found in the absence of exogenous GTP. In extracts from young brains, the increase in absorbance at 350 nm, which reflects the assembly reaction, was characterized by three phases (lag, elongation, and steady state) superimposed on a slow continuous increase due to non-specific aggregation. However, assembly in extracts from old brains, was very sluggish, in some cases barely more rapid than the non-specific aggregation reaction. Two to three times as much protein was assembled into cold-labile microtubules in extracts from young brains than from old brains. When 1 mM GTP was included in the assembly solutions the patterns of assembly in extracts from young and old brains became similar, with about the same amount of protein assembled into cold-labile microtubules. The assembly of tubulin purified from rat brains showed no differences between young and old. Results showed that extracts from old brains contained a higher GTPase activity than extracts from young brains. The sluggish assembly in extracts from old brains could be due to a deficiency in GTP or an inefficient regeneration of GTP.
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PMID:A comparison of microtubule assembly in brain extracts from young and old rats. 847 79

RHO3 encodes a Rho-type small GTPase of the yeast Saccharomyces cerevisiae. We isolated temperature-sensitive alleles and a dominant active allele of RHO3. Ts- rho3 cells lost cell polarity during bud formation and grew more isotropically than wild-type cells at nonpermissive temperatures. In contrast, cells carrying a dominant active mutant RHO3 displayed cold sensitivity, and the cells became elongated and bent, often at the position where actin patches were concentrated. These phenotypes of the rho3 mutants strongly suggest that RHO3 is involved in directing the growing points during bud formation. In addition, we found that SRO6, previously isolated as a multicopy suppressor of rho3, is the same as SEC4. The sec4-2 mutation was synthetic lethal with temperature-sensitive rho3 mutations and suppressed the cold sensitivity caused by a dominant active mutant RHO3. The genetic interactions between RHO3 and SEC4, taken together with the fact that the Rab-type GTPase Sec4p is required to fuse secretory vesicles together with plasma membrane for exocytosis, support a model in which the Rho3p pathway modulates morphogenesis during bud growth via directing organization of the actin cytoskeleton and the position of the secretory machinery for exocytosis.
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PMID:Genetic analysis of the Saccharomyces cerevisiae RHO3 gene, encoding a rho-type small GTPase, provides evidence for a role in bud formation. 885 36

In order to identify a protein interacting with RCC1, a guanine nucleotide-exchange factor for the nuclear GTPase Ran, we isolated a series of cold-sensitive suppressors of mtr1-2, a temperature-sensitive mutant of the Saccharomyces cerevisiae RCC1 homologue. One of the isolated suppressor mutants was mutated in the putative GTPase Gtr1p, being designated as gtr1-11. It also suppressed other alleles of mtr1-2, srm1-1 and prp20-1 in contrast to overexpression of the S. cerevisiae Ran/TC4 homologue Gsp1p, previously reported to suppress prp20-1, but not mtr1-2 or srm1-1. Furthermore, gtr1-11 suppressed the rna1-1, temperature-sensitive mutant of the Gsp1p GTPase-activating protein, but not the srp1-31, temperature-sensitive mutant of the S. cerevisiae importin alpha homologue. mtr1-2, srm1-1 and prp20-1 were also suppressed by overexpression of the mutated Gtr1p, Gtr1-11p. In summary, Gtr1p that was localized in the cytoplasm by immunofluoresence staining was suggested to function as a negative regulator for the Ran/TC4 GTPase cycle.
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PMID:Putative GTPase Gtr1p genetically interacts with the RanGTPase cycle in Saccharomyces cerevisiae. 888 81

The dnaG gene of Escherichia coli encodes the primase protein, which synthesizes a short pRNA that is essential for the initiation of both leading and lagging strand DNA synthesis. Two temperature-sensitive mutations in the 3' end of the dnaG gene, dnaG2903 and parB, cause a defect in chromosome partitioning at the nonpermissive temperature 42 degrees. We have characterized 24 cold-sensitive suppressor mutations of these two dnaG alleles. By genetic mapping and complementation, five different classes of suppressors have been assigned; sdgC, sdgD, sdgE, sdgG and sdgH. The genes responsible for suppression in four of the five classes have been determined. Four of the sdgC suppressor alleles are complemented by the dnaE gene, which encodes the enzymatic subunit of DNA polymerase III. The sdgE class are mutations in era, an essential GTPase of unknown function. The sdgG suppressor is likely a mutation in one of three genes: ubiC, ubiA or yjbI. The sdgH class affects rpsF, which encodes the ribosomal protein S6. Possible mechanisms of suppression by these different classes are discussed.
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PMID:Isolation and characterization of suppressors of two Escherichia coli dnaG mutations, dnaG2903 and parB. 909 42


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