| modification | 1. A nonhereditary change in an organism; e.g., one that is acquired from its own activity or environment. 2. A chemical or structural alteration in a molecule. Behaviour modification, the systematic use of principles of conditioning and learning, especially operant or instrumental conditioning, to teach certain skills or to extinguish undesirable behaviours, attitudes, or phobias. Chemical modification, alteration in the structure of a molecule, typically a macromolecule such as a protein, by chemical means; often, the covalent addition by some reagent. Covalent modification, alteration in the structure of a macromolecule by enzymatic means, resulting in a change in the properties of that macromolecule; frequently, this type of modification is physiologically relevant. (05 Mar 2000) |
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| modification enzyme | <enzyme, molecular biology> An enzyme that introduces minor bases into DNA or RNA or that alters bases already incorporated. Serves to alter the sequence so that restriction enzymes will not damage the strand. (18 Nov 1997) |
| post-translational modification | The enzymatic processing of a polypeptide chain after translation from messenger RNA and after peptide bond formation has occurred. Examples include glycosylation, acylation, limited proteolysis, phosphorylation, isoprenylation. (10 Oct 1997) |
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| ScrFI modification methylase | <enzyme> From lactococcus lactis subsp. Cremoris uc503; recognises sequence ccngg and forms m(5)ccngg; see also DNA modification methylase dsav and DNA modification methylase ssoii Registry number: EC 2.1.1.- Synonym: scrfi methylase (26 Jun 1999) |
| host restriction-modification | A bacterial system where the bacterium is able to destroy invading DNA from a bacteriophage (virus which infects bacteria) while at the same time preventing the destruction of their own DNA. The phage DNA is cleaved by a restriction enzyme made by the bacterium, the bacterial DNA is modified (usually with methylation) so that the enzyme will not destroy it. (09 Oct 1997) |
| Stirling's modification of Gram's stain | <technique> A stable aniline-crystal violet stain. (05 Mar 2000) |
| 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 restriction-modification enzymes | Systems consisting of two enzymes, a modification methylase and a restriction endonuclease. They are closely related in their specificity and protect the DNA of a given bacterial species. The methylase adds methyl groups to adenine or cytosine residues in the same target sequence that constitutes the restriction enzyme binding site. The methylation renders the target site resistant to restriction, thereby protecting DNA against cleavage. (12 Dec 1998) |