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51.
52.
The recombinant enzyme binase II was isolated from the culture liquid of Bacillus subtilis 3922 transformed with the pJF28 plasmid bearing the birB gene. The procedure of the enzyme purification included precipitation by polyethylene glycol with subsequent chromatography on DEAE-cellulose, heparin-Sepharose, and Toyopearl TSK-gel. The enzyme was purified 142-fold yielding a preparation with specific activity 1633 U/mg. The molecular weight of binase II is 30 kD. The enzyme is activated by Mg2+ and virtually completely inhibited by EDTA. The pH optimum for the reaction of RNA hydrolysis is 8.5. The properties of the enzyme are close to those of RNase Bsn from B. subtilis. The character of cleaving of synthetic single- and double-stranded polyribonucleotides by binase II suggests that the enzyme binds the substrate in the helix conformation, and its catalytic mechanism is close to that of RNase VI from cobra venom. 相似文献
53.
54.
S-RNases and sexual incompatibility: structure, functions, and evolutionary perspectives 总被引:3,自引:0,他引:3
S-RNase-based gametophytic self-incompatibility appears to be the most phylogenetically widespread form of self-incompatibility found in the angiosperms, having been reported in the Solanaceae, Scrophulariaceae, and Rosaceae. This intraspecific breeding barrier is controlled by a single genetic locus termed S. Rejection of self-pollen has been shown to be mediated in the pistil by a highly polymorphic series of ribonucleases, but as yet the pollen component of this recognition system has not been identified. Here we review our present knowledge concerning the structure, functions, and evolution of S-RNases and the S-loci in which they reside. In addition we present two new phylogenetic analyses of S-RNases which suggest that (1). sequence variability between S-alleles is spread across the whole gene and is not as clustered as is generally believed and (2). there is evidence of recombination and/or diversifying selection in two distinct regions of S-RNases. The implications of these findings are discussed. 相似文献
55.
Cort JR Yee A Edwards AM Arrowsmith CH Kennedy MA 《Journal of structural and functional genomics》2000,1(1):15-25
The solution structure of MTH1175, a 124-residue protein from the archaeon Methanobacterium thermoautotrophicum has been determined
by NMR spectroscopy. MTH1175 is part of a family of conserved hypothetical proteins (COG1433) with unknown functions which
contains multiple paralogs from all complete archaeal genomes and the archaeal gene-rich bacterium Thermotoga maritima. Sequence
similarity indicates this protein family may be related to the nitrogen fixation proteins NifB and NifX. MTH1175 adopts an
α/β topology with a single mixed β-sheet, and contains two flexible loops and an unstructured C-terminal tail. The fold resembles
that of Ribonuclease H and similar proteins, but differs from these in several respects, and is not likely to have a nuclease
activity.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
56.
Based on the tertiary structure of the ribosome-inactivating protein alpha-sarcin, domains that are responsible for hydrolyzing ribosomes and naked RNA have been dissected. In this study, we found that the head-to-tail interaction between the first amino beta-strand and the last carboxyl beta-strand is not involved in catalyzing the hydrolysis of ribosomes or ribonucleic acids. Instead, a four-strand pleated beta-sheet is indispensable for catalyzing both substrates, suggesting that alpha-sarcin and ribonuclease T1 (RNase T1) share a similar catalytic center. The integrity of an amino beta-hairpin and that of the loop L3 in alpha-sarcin are crucial for recognizing and hydrolyzing ribosomes in vitro and in vivo. However, a mutant protein without the beta-hairpin structure, or with a disrupted loop L3, is still capable of digesting ribonucleic acids. The functional involvement of the beta-hairpin and the loop L3 in the sarcin stem/loop RNA of ribosomes is demonstrated by a docking model, suggesting that the two structures are in essence naturally designed to distinguish ribosome-inactivating proteins from RNase T1 to inactivate ribosomes. 相似文献
57.
Secondary structure is evaluated for determining evolutionary relationships between catalytic RNA molecules that are so distantly
related they are scarcely alignable. The ribonucleoproteins RNase P (P) and RNase MRP (MRP) have been suggested to be evolutionarily
related because of similarities in both function and secondary structure. However, their RNA sequences cannot be aligned with
any confidence, and this leads to uncertainty in any trees inferred from sequences. We report several approaches to using
secondary structures for inferring evolutionary trees and emphasize quantitative tests to demonstrate that evolutionary information
can be recovered. For P and MRP, three hypotheses for the relatedness are considered. The first is that MRP is derived from
P in early eukaryotes. The next is that MRP is derived from P from an early endosymbiont. The third is that both P and MRP
evolved in the RNA-world (and the need for MRP has since been lost in prokaryotes). Quantitative comparisons of the pRNA and
mrpRNA secondary structures have found that the possibility of an organellar origin of MRP is unlikely. In addition, comparison
of secondary structures support the identity of an RNase P–like sequence in the maize chloroplast genome. Overall, it is concluded
that RNA secondary structure is useful for evaluating evolutionary relatedness, even with sequences that cannot be aligned
with confidence.
Received: 19 July 1999 / Accepted: 3 May 2000 相似文献
58.
Senescence-induced RNases in tomato 总被引:18,自引:0,他引:18
59.
Rafal Tomecki Katja M Larsen Roman J Szczesny Karolina Drazkowska Jens S Andersen Piotr P Stepien Andrzej Dziembowski Torben Heick Jensen 《The EMBO journal》2010,29(14):2342-2357
The eukaryotic RNA exosome is a ribonucleolytic complex involved in RNA processing and turnover. It consists of a nine‐subunit catalytically inert core that serves a structural function and participates in substrate recognition. Best defined in Saccharomyces cerevisiae, enzymatic activity comes from the associated subunits Dis3p (Rrp44p) and Rrp6p. The former is a nuclear and cytoplasmic RNase II/R‐like enzyme, which possesses both processive exo‐ and endonuclease activities, whereas the latter is a distributive RNase D‐like nuclear exonuclease. Although the exosome core is highly conserved, identity and arrangements of its catalytic subunits in different vertebrates remain elusive. Here, we demonstrate the association of two different Dis3p homologs—hDIS3 and hDIS3L—with the human exosome core. Interestingly, these factors display markedly different intracellular localizations: hDIS3 is mainly nuclear, whereas hDIS3L is strictly cytoplasmic. This compartmental distribution reflects the substrate preferences of the complex in vivo. Both hDIS3 and hDIS3L are active exonucleases; however, only hDIS3 has retained endonucleolytic activity. Our data suggest that three different ribonucleases can serve as catalytic subunits for the exosome in human cells. 相似文献
60.
Krastyu G. Ugrinov 《Biophysical journal》2010,98(7):1312-1320
Protein sequences evolved to fold in cells, including cotranslational folding of nascent polypeptide chains during their synthesis by the ribosome. The vectorial (N- to C-terminal) nature of cotranslational folding constrains the conformations of the nascent polypeptide chain in a manner not experienced by full-length chains diluted out of denaturant. We are still discovering to what extent these constraints affect later, posttranslational folding events. Here we directly address whether conformational constraints imposed by cotranslational folding affect the partitioning between productive folding to the native structure versus aggregation. We isolated polyribosomes from Escherichia coli cells expressing GFP, analyzed the nascent chain length distribution to determine the number of nascent chains that were long enough to fold to the native fluorescent structure, and calculated the folding yield for these nascent chains upon ribosome release versus the folding yield of an equivalent concentration of full-length, chemically denatured GFP polypeptide chains. We find that the yield of native fluorescent GFP is dramatically higher upon ribosome release of nascent chains versus dilution of full-length chains from denaturant. For kinetically trapped native structures such as GFP, folding correctly the first time, immediately after release from the ribosome, can lead to lifelong population of the native structure, as opposed to aggregation. 相似文献