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排序方式: 共有209条查询结果,搜索用时 156 毫秒
1.
2.
The proofreading of hydroxy analogues of leucine and isoleucine by leucyl-tRNA synthetases from E. coli and yeast. 总被引:3,自引:0,他引:3
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Three analogues each of leucine and isoleucine carrying hydroxy groups in gamma- or delta- or gamma- and delta-position have been synthesized, and tested in the aminoacylation by leucyl-tRNA synthetases from E. coli and yeast. Hydrolytic proofreading, as proposed in the chemical proofreading model, of these analogues and of homocysteine should result in a lactonisation of these compounds and therefore provide information regarding the proofreading mechanism of the two leucyl-tRNA synthetases. Leucyl-tRNA synthetase from E. coli shows a high initial substrate discrimination. Only two analogues, gamma-hydroxyleucine and homocysteine are activated and transferred to tRNALeu where a post-transfer proofreading occurs. Lactonisation of gamma-hydroxyleucine and homocysteine could be detected. Leucyl-tRNA synthetase from yeast has a relatively poor initial discrimination of these substrates, which is compensated by a very effective pre-transfer proofreading on the aminoacyl-adenylate level. No lactonisation nor mischarged tRNALeu is detectable. 相似文献
3.
A presumptive tetrasomy for the short arm of chromosome 9 总被引:3,自引:0,他引:3
4.
Isoleucine and Valine Metabolism in Escherichia coli K-12: Detection and Measurement of ilv-Specific Messenger Ribonucleic Acid 总被引:13,自引:11,他引:2
Ribonucleic acid-deoxyribonucleic acid (RNA-DNA) hybridization was employed for the determination of messenger RNA transcribed from the ilv gene cluster of Escherichia coli K-12. Strains with derepressed levels of the isoleucine and valine biosynthetic enzymes owing to linked or unlinked genetic lesions were found to exhibit ilv messenger RNA levels from 1.5- to 4-fold higher than did their isogenic parents. When grown under conditions that specifically repressed the synthesis of isoleucine- and valine-forming enzymes, most strains exhibited drastically reduced ilv messenger RNA levels. Hybridization performed with the separated strands of ilv DNA showed that all the ilv genes are transcribed from the same strand, the "l strand" of lambdaphi80CI857St68dilv DNA. Sucrose gradient analyses of RNA extracted from cells starved for isoleucine, valine, or leucine resulted in the detection of at least two distinct types of ilv messenger RNA. 相似文献
5.
Mathias Sprinzl Karl-Heinz Scheit Hans Sternbach Friedrich von der Haar Friedrich Cramer 《Biochemical and biophysical research communications》1973,51(4):881-887
2′-Deoxyadenosine and 3′-deoxyadenosine (cordycepin) can be incorporated into the 3′-terminal position of tRNAPhe by tRNA nucleotidyl transferase. tRNAPhe-C-C-2′dA and tRNAPhe-C-C-3′dA, missing the cis-diol group at the 3′-terminal end are resistant to periodate oxidation and are not able to form borate complexes. In aminoacylation experiments only the tRNAPhe-C-C-3′dA proved to be chargeable. 相似文献
6.
7.
8.
Characterization of a highly structured domain in Tbp2 from Neisseria meningitidis involved in binding to human transferrin. 总被引:6,自引:0,他引:6
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The binding of iron-loaded human transferrin at the surface of Neisseria meningitidis is mediated by two polypeptides, Tbp1 and Tbp2. Predicted Tbp amino acid sequences from N. meningitidis strains are highly divergent. This variability is particularly pronounced throughout the Tbp2 polypeptide. In this study, a highly structured and extremely stable Tbp2 domain of about 270 to 290 amino acids which is involved in the binding to transferrin and whose position is well conserved has been characterized. The conservation of such a remarkable structure in a very divergent protein domain (there is only 43% amino acid identity within this region) suggests that is plays an essential biological role and raises a number of questions regarding tbp2 evolution. 相似文献
9.
Nielsen J; Peixoto AA; Piccin A; Costa R; Kyriacou CP; Chalmers D 《Molecular biology and evolution》1994,11(6):839-853
The region of the clock gene period (per) that encodes a repetitive tract
of threonine-glycine (Thr-Gly) pairs has been compared between Dipteran
species both within and outside the Drosophilidae. All the non-
Drosophilidae sequences in this region are short and present a remarkably
stable picture compared to the Drosophilidae, in which the region is much
larger and extremely variable, both in size and composition. The
accelerated evolution in the repetitive region of the Drosophilidae appears
to be mainly due to an expansion of two ancestral repeats, one encoding a
Thr-Gly dipeptide and the other a pentapeptide rich in serine, glycine, and
asparagine or threonine. In some drosophilids the expansion involves a
duplication of the pentapeptide sequence, but in Drosophila pseudoobscura
both the dipeptide and the pentapeptide repeats are present in larger
numbers. In the nondrosophilids, however, the pentapeptide sequence is
represented by one copy and the dipeptide by two copies. These observations
fulfill some of the predictions of recent theoretical models that have
simulated the evolution of repetitive sequences.
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10.
Purification and characterization of a novel extracellular Streptomyces lividans 66 enzyme inactivating fusidic acid.
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The wild-type strain Streptomyces lividans 66 is resistant against the steroid-like antibiotic fusidic acid. Comparative studies of the wild-type strain and a fusidic acid-sensitive mutant allowed the identification of an extracellular enzyme which inactivates fusidic acid. With the help of a combination of ultrafiltration and chromatographies with Phenyl-Sepharose and an anion exchanger, the enzyme was highly purified. Its apparent molecular mass is 48 kDa, its optimal activity ranges between 45 and 55 degrees C, and its optimal pH is 6.0 to 9.0. It is stimulated by neither monovalent nor divalent ions. The enzyme acts as a specific esterase which removes the acetyl group at C-16 from fusidic acid. The resulting intermediate is unstable, and spontaneous lactonization between C-21 and C-16 occurs rapidly. 相似文献