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1.
During K+ depletion of a mutant of Escherichiacoli which cannot concentrate this cation, protein synthesis is inhibited but RNA formation continues. The RNA produced during K+ depletion was analyzed by gel electrophoresis. It was found that 4S, 5S and 23S RNA were synthesized by K+-depleted cells whether uninfected or infected with phage T4. In addition, an RNA species moving close to 16S (presumably 17S) and material of about 6–10S were made during K+ depletion. These species of RNA were not evident in growing cells. Methylation of RNA is severely inhibited during K+ depletion.  相似文献   

2.
A new endoribonuclease activity, RNase F, was partially purified from Escherichia coli cells. This activity can cleave a precursor RNA molecule (of Species 1), isolated from T4 infected cells, in a specific site. This activity is different from the other three know processing endoribonucleases of E. coli RNase III, RNase E and RNase P.  相似文献   

3.
4.
The protein neurotoxin II from the venom of the scorpion Androctonusaustralis Hector was labeled with 125I by the lactoperoxidase method to a specific radioactivity of about 100 μCi/μg without loss of biological activity. The labeled neurotoxin binds specifically to a single class of non intereacting binding sites of high affinity (KD = 0.3 – 0.6 nM) and low capacity (4000 – 8000 sites/cell) to electrically excitable neuroblastoma cells. Relation of these sites to the action potential Na+ channel is derived from identical concentration dependence of scorpion toxin binding and increase in duration and amplitude of action potential. The protein neurotoxin II from the sea anemone Anemona sulcata also affects the closing of the action potential Na+ ionophore in nerve axons. The unlabelled sea anemone toxin modifies 125I-labeled scorpion toxin II binding to neuroblastoma cells by increasing the apparent KD for labeled scorpion toxin without modification of the number of binding sites. It is concluded that both Androctonus scorpion toxin II and Anemona sea anemone toxin II interact competitively with a regulatory component of the action potential Na+ channel.  相似文献   

5.
A temperature sensitive kanamycin (Km) resistant R plasmid, Rtsl, was found to confer cupric ion (Cu2+) resistance on its hosts in Escherichiacoli. At conjugal transfer, two kinds of segregants were obtained from Rtsl, i.e. Cu2+ resistant, Km sensitive and Km resistant, Cu2+ sensitive plasmids. Protein T existed in E.coli cells harboring Rtsl or the CurKms-plasmid. The inhibitory effect on the host cell growth at 43°C was observed with Rtsl+ or the KmrCus-plasmid+ cells. A relationship between these Rtsl derivatives and Rtsl in Proteusmirabilis which has been studied was discussed.  相似文献   

6.
A partially purified preparation of pyridine nucleotide transhydrogenase (E.C. 1.6.1.1.) (energy-independent) has been obtained from membranes of Escherichiacoli by means of deoxycholate extraction and DEAE-cellulose chromatography in the presence of Triton X-100. The enzyme was lipid-depleted by treating with cholate and ammonium sulfate. The preparation was reactivated by various phospholipids, in particular, bacterial cardiolipin and phosphatidyl glycerol. Phosphatidyl ethanolamine, the major phospholipid in the outer membrane of E.coli, was relatively ineffective in stimulating activity. The membrane-bound pyridine nucleotide transhydrogenase is slowly inhibited by N-ethylmaleimide. Protection against inhibition was achieved with NAD+ and NADP+, but NADPH served to accelerate the rate of inhibition.  相似文献   

7.
Chemically formylated Met-tRNAmMet and Met-tRNAfMet species from E.coli and yeast were tested for their capacity to serve as chain-initiators in a cell-free system from E.coli. In the presence of R 17 mRNA, initiation factors and E.coli ribosomes, all four Met-tRNAs could form functional initiation complexes as measured by ribosomal binding kinetics, fMet-puromycin formation and synthesis of a dipeptide fMet-Ala. Unformylated Met-tRNAfMet from E.coli displayed significantly less activity as a peptide chain-initiator than the formylated Met-tRNAmMet species from E.coli and yeast. Although the latter tRNAs were less effective initiators than the “physiological” initiator tRNAs, the data seem to indicate that a blocked α-amino group represents the major token of identification by which Met-tRNA is admitted to function in E.coli peptide chain initiation.  相似文献   

8.
Two proteins (A and B) from Escherichia coli are required for the synthesis of the NAD precursor quinolinate from aspartate and dihydroxyacetone phosphate. Mammalian liver contains a FAD linked protein which replaces E. coli B protein for quinolinate synthesis. D-aspartic acid but not L-aspartic acid is a substrate for quinolinic acid synthesis in a system composed of the B protein replacing activity of mammalian liver and E. coli A protein. In contrast the E. coli B protein-E. coli A protein quinolinate synthetase system requires L-aspartic acid as substrate. The previous report that L-aspartate was a substrate in the liver-E. coli system was due to contamination of commercially available [14C]L-aspartate with [14C]D-aspartate. These and other observations suggest that liver B protein is D-aspartate oxidase and E. coli B protein is L-aspartate oxidase.  相似文献   

9.
Energy-dependent concentrative uptake of 14CH3NH3+ by cells of Escherichia coli provides preliminary evidence for one or more transport systems for NH4+ uptake. NH4+, but not glutamic acid, inhibited the uptake of 14CH3NH3+. Varying the pH for the uptake assays exposed two apparent systems: one maximally functioning at pH 7 that was strongly inhibited by cyanide or by the uncoupler m-chlorophenyl carbonylcyanide hydrazone and another maximally functioning at pH 9 and resistant to cyanide or m-chlorophenyl carbonylcyanide hydrazone. Kinetic analysis showed considerable experimental variability from day to day. Often simple Michaelis-Menten kinetics were not followed, but NH4+ was reproducibly a stronger inhibitor of uptake of 14CH3NH3+ than was nonradioactive CH3NH3+.  相似文献   

10.
Mutants of E. coli defective in both phosphoenolpyruvate carboxykinase and phosphoenolpyruvate synthetase are unable to use C4-dicarboxylic acids such as succinate and malate as carbon and energy sources for growth. Revertants that have restored function for either one of these enzymes can grow in a malate-mineral medium, but at a reduced rate compared with the growth of wild-type cells. E. coli appears to use two pathways for synthesis of phosphoenolpyruvate from C4-dicarboxylic acids. One of these involves decarboxylation of oxalacetate catalyzed by phosphoenolpyruvate carboxykinase. The second pathway makes use of the combined action of malic enzyme and phosphoenolpyruvate synthetase.  相似文献   

11.
Hybrids were constructed between E. coli K12 unc? mutants uncoupled in oxidative phosphorylation, and thus defective in ATP biosynthesis, and an F′ plasmid carrying nitrogen fixation genes from Klebsiella pneumoniae. Examination of these hybrids showed that expression of nif+Kp genes in E. coli K12 does not require coupling of oxidative phosphorylation but needs the contribution of an anaerobic electron transport system involving fumarate reduction. The nifKp cluster of genes does not contain functions able to complement a defective Mg2+-ATPase aggregate but does contain a function(s) which appears to interact with the uncB? mutant over the formation of a redox system.  相似文献   

12.
E. coli cells grown to phosphate starvation incorporate 32PO4 unequally into the α position of the four ribonucleotide triphosphates during a short period of labeling. A method for determining the relative specific activities of nucleotides in RNA molecules synthesized under these conditions and correcting sequence data is described.  相似文献   

13.
Purified RNA polymerase, DNA polymerase III and unwinding protein of Escherichiacoli catalyze limited rifampicin sensitive fd or ØX 174 DNA-dependent DNA synthesis. A protein has been partially purified from E.coli which stimulates rifampicin sensitive dXMP incorporation in this system 20 to 30 fold. This protein also stimulates DNA synthesis catalyzed by DNA polymerases I and II; the stimulation occurs in reactions primed with natural and synthetic DNAs as well as RNA-DNA hybrids. The protein is not a product of the known dna genes. In contrast to the above system of purified enzymes, rifampicin sensitive dXMP incorporation in crude extracts of E.coli is specifically dependent on fd but not ØX 174 DNA. An additional factor has been isolated from extracts of E.coli which restores specificity to the purified rifampicin sensitive system by preventing ØX 174 DNA from serving as a template.  相似文献   

14.
We find an endonuclease of high specific activity in a purified mouse interferon preparation. The interferon was purified from Ehrlich ascites tumor cultures which were induced with Newcastle disease virus. It has a higher specific activity (1.5 × 109 NIH mouse reference standard interferon units/mg protein) than reported for any interferon preparation but is not homogeneous. We do not know if the endonuclease activity is due to a contaminating protein or to interferon. The endonuclease does not degrade in our conditions polyuridylic acid or double stranded reovirus RNA and does not inactivate the tRNA2Gln species from E. coli, or tRNAVal species or polysomes from mouse L cells. Endonuclease in as little as 0.5 ng protein of the interferon preparation degrades μg quantities of messenger RNA from mouse L cells, of encephalomyocarditis virus RNA and of in vitro-synthesized reo-virus messenger RNA at 37° in 1 hour. Further characteristics of the endonuclease and its possible relationship (if any) to interferon remain to be established.  相似文献   

15.
E.coli 70S ribosomes uniformly labeled invivo with 32PO4 were subjected to varying doses of u.v. radiation and then to the combined action of the RNases A and T1. Following these treatments the ribosomal proteins were separated by trichloroacetic acid precipitation from the noncovalently attached RNA degradation fragments. Subsequent two-dimensional gel electrophoresis and autoradiography of these proteins revealed that significant 32PO4 was associated with unique ribosomal proteins, L2 was among these.  相似文献   

16.
A thermostable protein that strongly inhibits the soluble E. coli D-alanine carboxypeptidase was isolated from a cell-free extract of E. coli B. The inhibitor was purified 140-fold by heat treatment, selective precipitation at pH 4.5, ion exchange chromatography on DEAE-cellulose and gel chromatography on Sephadex G-100. Inhibition of soluble D-alanine carboxypeptidase by this inhibitor is reversed by cations such as Mg++ or Na+ and abolished by digestion of the inhibitor with proteolytic enzymes. The inhibitor does not affect either the particulate D-alanine carboxypeptidase of E. coli or the growth of the bacteria.  相似文献   

17.
Whereas m1G, m2G, m22G, m7G, T, m1A, m5C and Cm methylase activities were found in total cell enzyme of Saccharomyces cerevisiae using under-methylated E. coli tRNA and E. coli B tRNA in reaction with or without Mg++, only m1G, m2G, m22G and T methylases occurred in mitochondria. Mitochondrial and cytoplasmic tRNA cannot be methylated by their homologous enzymes; only mitochondrial tRNA can be methylated in a heterologous reaction by total cell enzyme with formation of T, m5C, m1A and low amounts of m2G and m22G.  相似文献   

18.
DNA-free minicells of Escherichia coli will not allow growth of phage T-7, nor is RNA synthesis stimulated by phage infection. Thus, these miniature cells seem not to contain in vivo RNA polymerase activity. However, DNA-dependent RNA polymerase activity can be unmasked in extracts with poly(dA-T) and Mn2+. This activity may represent a cytoplasmic pool of inactive RNA polymerase in normal cells.  相似文献   

19.
An alkylating fragment derived by enzymatic cleavage of [35S]-(1,2-dichlorovinyl)-L-cysteine reacted, apparently covalently, with RNA isolated from E. coli, and from livers of the bovine calf, rat and rabbit. Transfer RNA was much more susceptible to alkylation than ribosomal RNA as revealed by gel filtration technique, and measurement of [35S] substitution into nucleotides. Unfractionated E. coli tRNA modified by such reaction accepted most amino acids to the same extent as control tRNA, although about 40% less acceptance was observed for L-histidine, L-serine and L-tyrosine. Study of ribosomal binding, however, indicated an impairment of codonanticodon interaction between synthetic polynucleotide messengers and amino acyl substituted, alkylated tRNA.  相似文献   

20.
Neomycin inhibits in vitro DNA dependent DNA and RNA synthesis catalyzed by DNA polymerase I and RNA polymerase from E. coli. The effect of the antibiotic is more pronounced towards DNA synthesis. The inhibition of DNA synthesis is competitive with template DNA, does not reverse with excess deoxynucleoside triphosphate, Mg2+ or enzyme E. coli DNA polymerase I. Neomycin does not reduce the number of potential 3′ -OH end or primer. It seems to shorten the size of the newly formed polynucleotide.  相似文献   

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