Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:3.1.30.2 (endonuclease)
18,621 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The number of rRNA genes in Mycobacterium bovis BCG was examined by Southern hybridization of end-labeled 5S, 16S, and 23S rRNAs with BamHI, PstI, and SalI digests of M. bovis BCG DNA. Each RNA probe gave only one radioactive band with three kinds of DNA digest. These results suggest that M. bovis BCG chromosomes may carry only a minimum set of rRNA genes. Hybridization of randomly labeled rRNAs with BamHI, PstI, SalI, BglII, and PvuII digests of DNA from the same organism supported these conclusions. The 6.4-kilobase-pair SalI fragment containing the entire structural genes for both 16S and 23S rRNAs was cloned into pBR322. The cloned fragment was characterized by restriction endonuclease mapping, DNA-RNA hybridization analysis, and the R-loop technique. The results indicated that the fragments contained rRNA genes in the following order: 16S, 23S, and 5S rRNA genes. No tRNA gene was detected in the spacer region between the 16S and 23S rRNA genes, but one was found downstream of the 23S rRNA and 5S rRNA genes.
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PMID:Organization of rRNA genes in Mycobacterium bovis BCG. 302 50

A 12.4 kbp HindIII chromosomal DNA fragment harbouring an apparently intact 9.2 kbp endogenous murine leukaemia virus (MuLV)-related proviral genome was isolated from an RFM/Un strain mouse by molecular cloning and designated pRFM #6. Nucleotide sequence analysis revealed the following characteristic features in the pRFM #6 provirus: a distinct 200 bp sequence in the long terminal repeat (LTR) mid-U3 region, a primer binding site for glutamine tRNA, a 3' pol region encoding an 'endonuclease' protein of 390 amino acids, and the mink cell focus-forming virus type-specific sequence at the 5' portion of the env gene. The 699 bp 5' LTR and 700 bp 3' LTR of pRFM #6 provirus were identical except for three base changes in the U3 'enhancer' region. At the cell-provirus DNA junction, 4 bp direct repeats were present. The proviral genome was found at the same chromosomal DNA site in BALB/c, AKR, C3H, CBA and RFM strain mice, but not in NFS/N or C57BL/6 strain mice.
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PMID:Characterization of a molecular clone of RFM/Un mouse chromosomal DNA that contains a full-length endogenous murine leukaemia virus-related proviral genome. 302 98

The leuX gene of Escherichia coli codes for a suppressor tRNA and forms a single gene operon containing its own promoter and Q-independent terminator. An analysis of the in vitro processing of leuX precursor revealed that the processing of the 5' end took place in a single-step reaction catalysed by RNase P while the 3' processing involved two successive reactions. The endonucleolytic cleavage activity of the 3' precursor sequence was found to copurify with RNase P. Heat inactivation of thermosensitive RNase P from two independent E. coli mutants abolished the cleavage activity of both the 5' and 3' ends. These results altogether suggest that RNase P carries the activity of 3' end cleavage as well as that of 5' processing. In the presence of Mg2+ alone, the leuX precursor was found to be self-cleaved at a site approximately 13 nt inside from the 5' end of mature tRNA. The self-cleaved precursor tRNA was no longer processed by the 3' endonuclease, suggesting that the 3' endonuclease recognizes a specific conformation of the precursor tRNA for action.
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PMID:A novel function of RNase P from Escherichia coli: processing of a suppressor tRNA precursor. 306 98

S. cerevisae tRNA introns interrupt the gene at a constant position in the anticodon loop. Pre-tRNAs are matured by an endonuclease and a ligase. The endonuclease alone can accurately release the intron from the pre-tRNA. Here, we investigate the mechanism of splice site selection by the endonuclease. We propose that it initially recognizes features in the mature domain common to all tRNAs. Once positioned on the enzyme, the splice sites are recognizable because they are a fixed distance from the mature domain. To test this hypothesis, we developed a system for synthesizing pre-tRNA by bacteriophage T7 RNA polymerase. To search for recognition sites, we made several mutations. Mutations of C56 and U8 strongly affect endonuclease recognition of pre-tRNA. With insertion and deletion mutations, we show that the anticodon stem determines splicing specificity. The sequence and structure of the intron are not strong determinants of splice site selection.
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PMID:Substrate recognition and splice site determination in yeast tRNA splicing. 314 Oct 64

To investigate the mechanism by which the purified Xenopus tRNA splicing endonuclease recognizes its splice sites, we utilized yeast pre-tRNA(3Leu) and pre-tRNA(Phe) variants constructed by in vitro mutagenesis. We found that the endonuclease interacts with conserved features of the mature tRNA domain. In particular, U8 and C56 may be examples of contact points between protein and RNA. Given that there are no conserved sequences at the splice junctions, the specificity of cutting at both splice sites is determined by the length of the anticodon stem. Although in general, the sequence of the intron is unimportant for splicing, there are some structural requirements.
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PMID:Site selection by the tRNA splicing endonuclease of Xenopus laevis. 318 Feb 24

We report on the properties of a partially purified tRNA intron endonuclease from the archaebacterium Halobacterium volcanii. This enzyme is capable of precise excision of the 104-nucleotide intron from halo-bacterial pre-tRNA(Trp) substrates generated in vitro by T7 RNA polymerase transcription. The reaction requires divalent cations (Mg2+ or Ca2+) or spermidine, is inhibited by monovalent cations, and produces 5'-hydroxyl and 2',3'-cyclic phosphate termini. Unlike the universal substrate recognition properties characteristic of the eukaryotic tRNA intron endonucleases, this enzyme is specific for halophilic tRNA(Trp) substrates. The partially purified enzyme is not capable of removing the intron from a yeast pre-tRNA(Phe) substrate. Analysis of the enzyme's ability to cleave tRNA(Trp) substrates lacking exon sequences demonstrated that the mature tRNA-like structure is not required in the substrate. A substrate retaining the intact intron and only the anticodon stem and loop exon regions was efficiently cleaved. Deletions within the intron indicated that the intron was not a primary site for recognition by the endonuclease; however, its presence affects the efficiency of the cleavage reaction. The possible relationship of this enzyme to other RNA endonucleases is discussed.
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PMID:A tRNA(Trp) intron endonuclease from Halobacterium volcanii. Unique substrate recognition properties. 319 21

Two unlinked mutations that alter the enzyme activity of tRNA-splicing endonuclease have been identified in yeast. The sen1-1 mutation, which maps on chromosome 12, causes temperature-sensitive growth, reduced in vitro endonuclease activity, and in vivo accumulation of unspliced pre-tRNAs. The sen2-1 mutation does not confer a detectable growth defect, but causes a temperature-dependent reduction of in vitro endonuclease activity. Pre-tRNAs do not accumulate in sen2-1 strains. The in vitro enzyme activities of sen1-1 and sen2-1 complement in extracts from a heterozygous diploid, but fail to complement in mixed extracts from separate sen1-1 and sen2-1 haploid strains. These results suggest a direct role for SEN gene products in the enzymatic removal of introns from tRNA that is distinct from the role of other products known to affect tRNA splicing.
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PMID:Mutations affecting the tRNA-splicing endonuclease activity of Saccharomyces cerevisiae. 328 87

The 5'- and 3'-tRNA processing nucleases have been isolated from rat liver mitochondria. The two activities co-purified through heparin-agarose and phenyl-Sepharose columns and then efficiently separated on a DEAE-cellulose column. The 5' processing nuclease was found in the flow-through fraction, and the 3' processing activity eluted with 0.5 M KCl. Both enzymes were greater than 500-fold purified over the high speed supernatant of a mitoplast extract. The 159-base pre-tRNATyr used as a substrate in this study was synthesized in vitro and contained the Escherichia coli suppressor III tRNATyr plus a 49-base leader sequence and a 25-base trailing sequence. The 5' processing nuclease converted the pre-tRNATyr into two discrete RNA species, identified as the 5'-processed intermediate and the 5' flanking fragment, by endonucleolytic cleavage at the 5' end of the mature tRNATyr sequence. The 3' processing nuclease was inactive with the intact pre-tRNATyr as substrate but efficiently converted the 5'-processed intermediate to the mature tRNATyr, indicating an obligatory order of processing in which 5' maturation was necessary before cleavage by the 3' processing nuclease could occur. The mitochondrial enzymes exhibited optimal activity in the presence of about 2 mM Mg2+, but both enzymes were nearly fully active without addition of exogenous Mg2+ to the reaction mixtures. In contrast, a partially purified 5' processing endonuclease present in the postmitochondrial cytosolic fraction required higher [Mg2+] for activity, thus providing a means for differentiating between these similar enzyme activities obtained from the cytosolic and mitochondrial fractions.
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PMID:Separation and characterization of 5'- and 3'-tRNA processing nucleases from rat liver mitochondria. 330 31

Yeast tRNA ligase is an enzyme required for tRNA splicing. A study by indirect immune fluorescence shows that this enzyme is localized in the cell nucleus. At higher resolution, studies using indirect immune electron microscopy show this nuclear location to be primarily at the inner membrane of the nuclear envelope, most likely at the nuclear pore. There is a more diffuse, secondary location of ligase in a region of the nucleoplasm within 300 nm of the nuclear envelope. When the amount of ligase in the cell is increased, nuclear staining increases but staining of the nuclear envelope remains constant. This experiment indicates that there are a limited number of ligase sites at the nuclear envelope. Since the other tRNA splicing component, the endonuclease, has the characteristics of an integral membrane protein, we hypothesize that it constitutes the site for the interaction of ligase with the nuclear envelope.
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PMID:The subnuclear localization of tRNA ligase in yeast. 331 32

Decanucleotide (Ap)6GpTpUpC and undecanucleotide GpApUpCpCp (Up)5U have been synthesised. They constitute 5'- and 3'-parts of a 21-mer which imitates T psi C-arm of yeast tRNA(Val1) and is a potential substrate for m1A-methylases and pseudouridine synthetase. The oligonucleotide blocks, synthesised enzymatically by means of ribonucleases of various substrate specificity and polynucleotide phosphorylases (TpUpC, ApUpCpC, pGpTpUpC, GpApUpCpC) or obtained by hydrolysis of poly(U) and poly(A) with Serratia marcescens endonuclease (hexauridilate and hexaadenilate), were joined by T4 RNA ligase.
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PMID:[Model substrates of enzymes modifying ribonucleic acids. Synthesis of deca- and undecanucleotid-fragments of 21-member oligoribonucleotide simulating T psi C-branch of yeast valine tRNA]. 344 71


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