Linked Life Data

8202083

Source:http://linkedlifedata.com/resource/pubmed/id/8202083

Statements in which the resource exists as a subject.
PredicateObject
rdf:type
lifeskim:mentions
pubmed:issue
4
pubmed:dateCreated
1994-7-5
pubmed:abstractText
O6-Methylguanine-DNA methyltransferase catalyzes transfer of a methyl group from O6-methylguanine and O4-methylthymine of DNA to a cysteine residue of the enzyme protein, thereby repairing the mutagenic and carcinogenic lesions in a single-step reaction. There are highly conserved amino acid sequences around the methyl-accepting cysteine site in eleven molecular species of methyltransferases. To elucidate the significance of the conserved sequence, amino acid substitutions were introduced by site-directed mutagenesis of the cloned DNA for Escherichia coli Ogt methyltransferase, and the activity and stability of mutant forms of the enzyme were examined. When cysteine-139, to which methyl transfer occurs, was replaced by other amino acids, all of the mutants showed the methyltransferase-negative phenotype. Methyltransferase-positive revertants, isolated from one of the negative mutants, had restored codons for cysteine. Thus the cysteine residue is essential for acceptance of the methyl group and is not replaceable by other amino acids. Using this negative and positive selection procedure, the analysis was extended to other residues near the acceptor site. At the histidine-140 and arginine-141 sites, all the positive revertants isolated carried codons for amino acids identical to those of the wild-type protein. At proline-138, five substitutions (serine, glutamine, threonine, histidine, and alanine) exhibited the positive phenotype but levels of methyltransferase activity in extracts of cells harboring these mutant forms were very low. This suggests that the proline residue at this site is important for maintaining the proper conformation of the protein. With valine-142 substitutions there were seven types of positive revertants, among which mutants carrying isoleucine, cysteine, leucine, and alanine showed relatively high levels of methyltransferase activity. These results indicate that the sequence Pro-Cys-His-Arg is a sine qua non for methyltransferase to exert its function.
pubmed:language
eng
pubmed:journal
pubmed:citationSubset
IM
pubmed:chemical
pubmed:status
MEDLINE
pubmed:month
May
pubmed:issn
0026-8925
pubmed:author
pubmed:issnType
Print
pubmed:day
25
pubmed:volume
243
pubmed:owner
NLM
pubmed:authorsComplete
Y
pubmed:pagination
379-89
pubmed:dateRevised
2006-11-15
pubmed:meshHeading
pubmed-meshheading:8202083-Alkylating Agents, pubmed-meshheading:8202083-Amino Acid Sequence, pubmed-meshheading:8202083-Arginine, pubmed-meshheading:8202083-Bacterial Proteins, pubmed-meshheading:8202083-Base Sequence, pubmed-meshheading:8202083-Blotting, Western, pubmed-meshheading:8202083-Consensus Sequence, pubmed-meshheading:8202083-Cysteine, pubmed-meshheading:8202083-DNA, Bacterial, pubmed-meshheading:8202083-DNA Repair, pubmed-meshheading:8202083-Escherichia coli, pubmed-meshheading:8202083-Escherichia coli Proteins, pubmed-meshheading:8202083-Histidine, pubmed-meshheading:8202083-Methylation, pubmed-meshheading:8202083-Methyltransferases, pubmed-meshheading:8202083-Molecular Sequence Data, pubmed-meshheading:8202083-Mutagenesis, Site-Directed, pubmed-meshheading:8202083-O(6)-Methylguanine-DNA Methyltransferase, pubmed-meshheading:8202083-Point Mutation, pubmed-meshheading:8202083-Proline, pubmed-meshheading:8202083-Sequence Analysis
pubmed:year
1994
pubmed:articleTitle
Requirement of the Pro-Cys-His-Arg sequence for O6-methylguanine-DNA methyltransferase activity revealed by saturation mutagenesis with negative and positive screening.
pubmed:affiliation
Department of Biochemistry, Faculty of Medicine, Kyushu University, Fukuoka, Japan.
pubmed:publicationType
Journal Article, Research Support, Non-U.S. Gov't