| MHC restriction | <immunology> Restriction on interaction between cells of the immune system because of the requirement to recognise foreign antigen is association with MHC antigens (major histocompatibility antigens). Thus, cytotoxic T-cells will only kill virally infected cells that have the same Class I antigens as themselves, whereas helper T-cells respond to foreign antigen associated with Class II antigens. (18 Nov 1997) |
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| 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) |
| DNA restriction enzymes | <enzyme> Enzymes that are part of the restriction-modification systems. They catalyze the endonucleolytic cleavage of DNA sequences which lack the species-specific methylation pattern in the host cell's DNA. Cleavage yields random or specific double-stranded fragments with terminal 5'-phosphates. The function of restriction enzymes is to destroy any foreign DNA that invades the host cell. most have been studied in bacterial systems, but a few have been found in eukaryotic organisms. They are also used as tools for the systematic dissection and mapping of chromosomes, in the determination of base sequences of dnas, and have made it possible to splice and recombine genes from one organism into the genome of another. Registry number: EC 3.1.21 (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) |
| ecori restriction enzyme | <enzyme, molecular biology> A commonly-used restriction enzyme (enzyme which will cleave the phosphodiester bonds of DNA at specific nucleotide sequences) that came from the bacteria Escherichia coli and recognises the sequence GAATTC. The enzyme will make a staggered cut of the double-stranded DNA molecule by cutting between the G and A on both strands. (09 Oct 1997) |
| lactase restriction | An inherited trait in which there is low lactase activity and thus there is defective lactose intestinal metabolism. Compare: lactase persistence. (05 Mar 2000) |
| allelic gene | See: allele, dominance of traits. (05 Mar 2000) |
| antibiotic resistance gene | Genes in a microorganism which confer resistance to antibiotics, for example by coding for enzymes which destroy it, by coding for surface proteins which prevent it from entering the microorganism, or by being a mutant form of the antibiotic's target so that it can ignore it. (09 Oct 1997) |
| autosomal gene | A gene located on any chromosome other than the sex chromosomes (X or Y). (05 Mar 2000) |
| bicoid gene | A group of genes which are important to the proper development of the head and thorax in the embryo of the fruit fly Drosophila melanogaster. (09 Oct 1997) |
| BRCA1 breast cancer susceptibility gene | This mutated (changed) version of the BRCA1 gene makes a person susceptible to developing breast cancer. (12 Dec 1998) |
| calcitonin gene-related peptide | <protein> A second product transcribed from the calcitonin gene. Calcitonin gene related peptide is found in a number of tissues including nervous tissue. It is a vasodilator that may participate in the cutaneous triple response. It is a neuropeptide of 37 amino acids with structural homology to salmon calcitonin. Co-localises with substance P in neurons. It occurs as a result of alternative processing of mRNA from the calcitonin gene. The neuropeptide is widely distributed in neural tissue of the brain, gut, perivascular nerves, and other tissue. The peptide produces multiple biological effects and has both circulatory and neurotransmitter modes of action. In particular, it is a potent endogenous vasodilator. Intracerebral administration leads to a rise in noradrenergic sympathetic outflow, a rise in blood pressure and a fall in gastric secretion. Acronym: CGRP (05 May 2002) |
| cancer susceptibility gene | tumour suppressor gene |
| rab gene | 1. <molecular biology> One of the three main groups of ras like genes specifying small GTP-binding proteins (the others are ras and rho). Rab proteins are involved in vesicular traffic and seem to control translocation from donor to acceptor membranes. 2. <cell biology> Gene family in plants responsive to abscisic acid: encode proteins of 15-17 kD. (18 Nov 1997) |
| pair rule gene | <molecular biology> A segmentation gene, expressed sequentially between gap genes and segment polarity genes. In development of Drosophila, a set of about 8 genes that are expressed only in alternate segments (odd or even) of the developing embryo. Loss of function mutants thus lack alternate segments. Examples: even skipped (eve), fushi tarazu (ftz), hairy. (18 Nov 1997) |