Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:6.5.1.2 (DNA ligase)
 2,749 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Predefined changes in a known DNA sequence were introduced by a general method. Oligodeoxyribonucleotides complementary to positions 582 to 593 of the viral DNA strand of the bacteriophage phiX174 am3 mutant (pGTATCCTACAAA), and to the wild type sequence in this region (pGTATCCTACAAA), were synthesized and used as specific mutagens. Each of these oligonucleotides was incorporated into a complete circular complementary strand when used as primer on a genetically heterologous viral strand template, by the combined action of subtilisin-treated Escherichia coli DNA polymerase I and T4 DNA ligase. Incomplete duplexes were removed or were inactivated by nuclease S1 and the products were used to transfect spheroplasts of E. coli. Both oligonucleotides induced specific mutations at high efficiency when used with heterologous template (15% mutants among progeny phage). The am phages isolated by this procedure are phenotypically gene E mutants, and contain A at position 587 of the viral strand. They thus appear identical with am3 and provide evidence that the change G leads to A at position 587 is sufficient to produce a defective E function. Since the template for the induction of am mutants carried another genetic marker (sB1), the strains carrying the induced mutations have the new genotype am3 sB1. It should be possible to introduce the am3 mutation into any known mutant strain of phi174 using this same oligonucleotide. Both possible transition mutations were induced in these experiments. In principle, the method could also induce transversions, insertions, and deletions. The method should be applicable to other circular DNAs of similar size, for example recombinant DNA plasmids.
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PMID:Mutagenesis at a specific position in a DNA sequence. 68 66

The ada gene of Escherichia coli encodes a 39-kDa protein which serves both as a transcriptional activator of the adaptive response to alkylating agents and as a DNA repair enzyme demethylating O6-methyl-guanine and phosphotriester residues. Here, the isolated Ada protein was found to be readily cleaved into two fragments of similar size by treatment with trypsin, chymotrypsin, subtilisin, or V8 protease. The fragments retained their respective methyltransferase activities. The Ada protein is, therefore, comprised of two stable active domains united by a central hinge region of about 10 amino acids. Post-translational modification of the Ada protein by methylation of a specific cysteine residue in the NH2-terminal domain is known to convert it to an efficient transcriptional activator. This residue has now been identified as Cys-69.
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PMID:Functional domains and methyl acceptor sites of the Escherichia coli ada protein. 316 36