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)

We have analyzed the restriction digest patterns of the mitochondrial DNA from 41 cytoplasmic petite strains of Saccharomyces cerevisiae, that have been extensively characterized with respect to genetic markers. Each mitochondrial DNA was digested with seven restriction endonucleases (EcoRI, HPaI, HindIII, BamHI, HhaI, SalI, and PstI) which together make 41 cuts in grande mitochondrial DNA and for which we have derived fragment maps. The petite mitochondrial DNAs were also analyzed with HpaII, HaeIII, and AluI, each of which makes more than 80 cleavages in grande mitochondrial DNA. On the basis of the restriction patterns observed (i.e., only one fragment migrating differently from grande for a single deletion, and more than one for multiple deletions) and by comparing petite and grande mitochondrial DNA restriction maps, the petite clones could be classified into two main groups: (1) petites representing a single deletion of grande mitochondrial DNA and (2) petites containing multiple deletions of the grande mitochondrial DNA resulting in rearranged sequences. Single deletion petites may retain a large portion of the grande mitochondrial genome or may be of low kinetic cimplexity. Many petites which are scored as single continuous deletions by genetic criteria were later demonstrated to be internally deleted by restriction endonuclease analysis. Heterogeneous sequences, manifested by the presence of sub-stoichiometric amounts of some restriction fragments, may accompany the single or multiple deletions. Single deletions with heterogeneous sequences remain useful for mapping if the low concentration sequences represent a subset of the stoichiometric bands. Using a group of petites which retain single continuous regions of the grande mitochondrial DNA, we have physically mapped antibiotic resistance and mit- markers to regions of the grande restriction map as follows: C (99.3--1.4 map units)--OXI-1 (2.5--15.7)--OXI-2 (18.5--25)--P (28.1--34.2)--OXI-3 (32.2--61.2--OII (60--62)--COB (64.6--80.8--0I (80.4--85.7)--E (95--98.9).
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PMID:Restriction enzyme analysis of mitochondrial DNAs of petite mutants of yeast: classification of petites, and deletion mapping of mitochondrial genes. 35 53

Cbp1p is a nuclear encoded protein required for the stabilization of mitochondrial COB mRNA, which codes for apocytochrome b in the yeast Saccharomyces cerevisiae. The COB gene is cotranscribed with the upstream tRNA(Glu) gene. Release of tRNA(Glu) from the initial transcript generates a precursor mRNA with a 5'-end at position -1098. The 5'-end of mature COB message is generated by cleavage of the pre-mRNA at nucleotide -955 or -954. Previous work indicated that Cbp1p acts through cis-elements near these cleavage sites. Here we have tested whether Cbp1p stabilizes COB mRNA solely by stimulating the processing of COB precursor RNA at nucleotide -955/-954. Yeast strain TG955 was constructed such that the -955 COB mRNA 5'-processing site coincides with the upstream tRNA 3'-endonuclease site at position -1098, allowing the 5'-end of COB mRNA to be formed by the tRNA 3'-processing enzyme. Respiratory growth and stability of COB mRNA in TG955 are Cbp1p-dependent. Therefore, we conclude that Cbp1p is important for the stabilization of COB mRNA after 5'-processing.
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PMID:Cbp1p is required for message stability following 5'-processing of COB mRNA. 820 74

A large number of group I introns encode a family of homologous proteins that either promote intron splicing (maturases) or are site-specific DNA endonucleases that function in intron mobility (a process called "homing"). Genetic studies have shown that some of these proteins have both activities, yet how a single protein carries out both functions remains obscure. The similarity between respective DNA-binding sites and the RNA structure near the 5' and 3' splice sites has fueled speculation that such proteins may use analogous interactions to perform both functions. The Aspergillus nidulans mitochondrial COB group I intron encodes a bi-functional protein, I-AniI, that has both RNA maturase and site-specific DNA endonuclease activities in vitro. Here, we show that I-AniI shows distinctive features of the endonuclease family to which it belongs, including highly specific, tight binding and sequential DNA strand cleavage. Competition experiments demonstrate that I-AniI binds the COB intron RNA even in saturating concentrations of its DNA target site substrate, suggesting that the protein has a separate binding site for RNA. In addition, we provide evidence that two different DNA-binding site mutants of I-AniI have little effect on the protein's RNA maturation activity. Since RNA splicing is likely a secondary adaptation of the protein, these observations support a model in which homing endonucleases may have developed maturase function by utilizing a hitherto "non-functional" protein surface.
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PMID:Functionally distinct nucleic acid binding sites for a group I intron encoded RNA maturase/DNA homing endonuclease. 1275 73

Group I introns are thought to be self-propagating mobile elements, and are distributed over a wide range of organisms through horizontal transmission. Intron invasion is initiated through cleavage of a target DNA by a homing endonuclease encoded in an open reading frame (ORF) found within the intron. The intron is likely of no benefit to the host cell and is not maintained over time, leading to the accumulation of mutations after intron invasion. Therefore, regular invasional transmission of the intron to a new species at least once before its degeneration is likely essential for its evolutionary long-term existence. In many cases, the target is in a protein-coding region which is well conserved among organisms, but contains ambiguity at the third nucleotide position of the codon. Consequently, the homing endonuclease might be adapted to overcome sequence polymorphisms at the target site. To address whether codon degeneracy affects horizontal transmission, we investigated the recognition properties of a homing enzyme, I-CsmI, that is encoded in the intronic ORF of a group I intron located in the mitochondrial COB gene of the unicellular green alga Chlamydomonas smithii. We successfully expressed and purified three types of N-terminally truncated I-CsmI polypeptides, and assayed the efficiency of cleavage for 81 substrates containing single nucleotide substitutions. We found a slight but significant tendency that I-CsmI cleaves substrates containing a silent or tolerated amino acid change more efficiently than nonsilent or nontolerated ones. The published recognition properties of I-SpomI, I-ScaI, and I-SceII were reconsidered from this point of view, and we detected proficient adaptation of I-SpomI, I-ScaI, and I-SceII for target site sequence degeneracy. Based on the results described above, we propose that intronic homing enzymes are adapted to cleave sequences that might appear at the target region in various species, however, such adaptation becomes less prominent in proportion to the time elapsed after intron invasion into a new host.
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PMID:Adaptation of intronic homing endonuclease for successful horizontal transmission. 1588 98

The details of mRNA maturation in Saccharomyces mitochondria are not well understood. All seven mRNAs are transcribed as part of multigenic units. The mRNAs are processed at a common 3'-dodecamer sequence, but the 5'-ends have seven different sequences. To investigate whether apocytochrome b (COB) mRNA is processed at the 5'-end from a longer precursor by an endonuclease or an exonuclease, a 64-nucleotide sequence, which is required for the protection of COB mRNA by the Cbp1 protein and is found at the 5'-end of the processed COB mRNA, was duplicated in tandem. The wild-type 64-nucleotide element functioned in either the upstream or downstream position when paired with a mutant element. In the tandem wild-type strain, the 5'-end of the mRNA was at the 5'-end of the upstream unit, demonstrating that the mRNA is processed by an exonuclease. Accumulation of precursor COB RNA in single and double element strains with a deletion of PET127 demonstrated that the encoded protein governs the 5'-exonuclease responsible for processing the precursor to the mature form.
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PMID:Pet127 governs a 5' -> 3'-exonuclease important in maturation of apocytochrome b mRNA in Saccharomyces cerevisiae. 1808 65