| DNA methylation | <molecular biology> Process by which methyl groups are added to certain nucleotides in genomic DNA. This affects gene expression, as methylated DNA is not easily transcribed. The degree of methylation is passed on to daughter strands at mitosis by maintainance DNA methylases. Accordingly, DNA methylation is thought to play an important developmental role in sequentially restricting the transcribable genes available to distinct cell lineages. In bacteria, methylation plays an important role in the restriction systems, as restriction enzymes cannot cut sequences with certain specific methylations. (18 Nov 1997) |
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| DNA, mitochondrial | Double-stranded DNA of mitochondria. In eukaryotes, the mitochondrial genome is circular and codes for ribosomal rnas, transfer rnas, and about 10 proteins. (12 Dec 1998) |
| DNA modification | <molecular biology> A variety of chemical changes made to a DNA molecule just after it has been replicated. An example is DNA methylation. (09 Oct 1997) |
| DNA modification methylases | <enzyme> Enzymes that are part of the restriction-modification systems. They are responsible for producing a species-characteristic methylation pattern, on either adenine or cytosine residues, in a specific short base sequence in the host cell's own DNA. This methylated sequence will occur many times in the hosT-cell DNA and remain intact for the lifetime of the cell. Any DNA from another species which gains entry into a living cell and lacks the characteristic methylation pattern will be recognised by the restriction endonucleases of similar specificity and destroyed by cleavage. most have been studied in bacterial systems, but a few have been found in eukaryotic organisms. Registry number: EC 2.1.1.- (12 Dec 1998) |
| DNA molecules, recombinant | A combination of DNA molecules of different origin that are joined using recombinant DNA technology. (12 Dec 1998) |
| DNA mutational analysis | Biochemical identification of mutational changes in a nucleotide sequence. (12 Dec 1998) |
| DNA, neoplasm | DNA present in neoplastic tissue. (12 Dec 1998) |
| DNA N-glycosidase | <enzyme> Excises 3-methyladenine from alkylated DNA leaving an apurinic site with both 3' and 5' phosphodiester bonds intact, a preparatory step for nucleotide excision repair; excises hypoxanthine from deaminated DNA and polydeoxyribonucleotides; prefer EC 3.2.2.20 or EC 3.2.2.21 Registry number: EC 3.2.2.- Synonym: DNA glycosylase, methylpurine DNA glycosylase (26 Jun 1999) |
| DNA, nongenetic | Through the marvellous medium of the Internet, we have discovered that DNA need not refer to deoxyribonucleic acid. Specifically, in an e-mail entitled A day in the life of a specialist registrar from Glascow, Scotland we read that in gynaecology outpatient clinic, the specialist registrar (resident in the U.S.) at 12:10 Sorted out the DNA's (did not attends). We in the U. S. Might say the no-show when a patient does not present for his/her appointment. (12 Dec 1998) |
| DNA nucleotidylexotransferase | <enzyme> A non-template-directed DNA polymerase normally found in vertebrate thymus and bone marrow. It catalyses the elongation of oligo- or polydeoxynucleotide chains and is widely used as a tool in the differential diagnosis of acute leukaemias in man. Chemical name: Nucleoside-triphosphate:DNA deoxynucleotidylexotransferase Registry number: EC 2.7.7.31 (12 Dec 1998) |
| DNA nucleotidyltransferases | <enzyme> A general term denoting enzymes that catalyze the template-directed incorporation of deoxyribonucleotides into a DNA chain. Registry number: EC 2.7.7.- (12 Dec 1998) |
| DNA photolyase | <enzyme, molecular biology> A DNA repair enzyme which recognises and removes dimers that have formed between pyrimidine nitrogenous bases on the same strand as each other, as a result of too much ultraviolet radiation. The enzyme can only do this if visible light is present. (09 Oct 1997) |
| DNA, plant | Deoxyribonucleic acid that makes up the genetic material of plants. (12 Dec 1998) |
| DNA polymerase | <enzyme, molecular biology> Enzymes involved in template directed synthesis of DNA from deoxyribonucleotide triphosphates. I, II and III are known in E. Coli, III appears to be most important in genome replication and I is important for its ability to edit out unpaired bases at the end of growing strands. Animal cells have and polymerases, with apparently responsible for replication of nuclear DNA and for replication of mitochondrial. All these function with a DNA strand as template. Retroviruses possess a unique DNA polymerase (reverse transcriptase) that uses an RNA template. (18 Nov 1997) |
| DNA polymerase beta | <enzyme> A DNA repair enzyme that catalyses DNA synthesis during base excision DNA repair. Registry number: EC 2.7.7.- (12 Dec 1998) |