| deoxyribonucleases, type I site-specific | <enzyme> Enzyme systems containing three different subunits and requiring ATP, s-adenosylmethionine, and magnesium for endonucleolytic activity to give random double-stranded fragments with terminal 5'-phosphates. They function also as DNA-dependent atpases and modification methylases, catalyzing the reactions of EC 2.1.1.72 and EC 2.1.1.73 with similar site-specificity. The systems recognise specific short DNA sequences and cleave at sites remote from the recognition sequence. Enzymes from different microorganisms with the same specificity are called isoschizomers. Registry number: EC 3.1.21.3 (12 Dec 1998) |
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| DNA-(apurinic or apyrimidinic site) lyase | <enzyme> Formerly EC 3.1.25.2 Registry number: EC 4.2.99.18 Synonym: endodeoxyribonuclease (apurinic or apyrimidinic), apurinic endonuclease, apurinic DNA endonuclease, purine insertase, endonuclease iv, DNA repair endonuclease, endonuclease vi, endonuclease iv, E coli, bap1, bovine ap endonuclease I, nfo gene product, apci, apcii, apciii, ap lyase, ap endonuclease, hap1 DNA repair enzyme, apurine-apyrimidine endonuclease (26 Jun 1999) |
| DNAse i hypersensitivity site | <molecular biology> A site on a DNA molecule that is especially prone to being cut apart by the endonuclease enzyme DNase I, which breaks down DNA into smaller fragments by cleaving phosphodiester bonds. These sites tend to be near active genes, which are regularly transcribed. (09 Oct 1997) |
| trophoblastic tumour, placental site | A tumour that arises from the trophoblast of the placental bed and is composed mainly of cytotrophoblastic cells. It encompasses lesions of low- and high-grade malignancy. (holland et al., cancer medicine, 3d ed, p1691) (12 Dec 1998) |
| expression site | The location in the genome of the gene for the variable surface glycoprotein that is currently being expressed (an expression-linked copy) by the trypanosome (a parasitic protozoan which causes the disease African sleeping sickness). most of these sites are near the ends, or telomeres, of a chromosome. (09 Oct 1997) |
| upstream activation site | A DNA sequence that regulates transcription like an enhancer but does notwork if its located downstream from a promoter. (09 Oct 1997) |
| fragile site | Places on chromosomes that tend to break more often than other places. These places also tend to be where chromosomal translocations (a type of chromosomal mutation) occur. (09 Oct 1997) |
| ligand binding site | The site on a protein's surface that binds a ligand; equivalent to the active site if the ligand is the substrate of an enzyme. (05 Mar 2000) |
| bacteria-free stage of bacterial endocarditis | Endocarditis described prior to the antibiotic era and presumably due to spontaneous healing of the bacterial vegetations. (05 Mar 2000) |
| carbon dioxide-free water | Purified water that has been boiled vigorously for 5 minutes or more. (05 Mar 2000) |
| radical, free | In biochemistry, it is a group of atoms bonded together into an entity that is extremely reactive and shortlived. (a free radical is not a political extremist on parole.) (12 Dec 1998) |
| germ-free animal | An animal which has no microorganisms whatsoever living in or on it. An animal which was born and raised in an isolated environment with no microorganisms in it, such as within a germ-free isolator. (09 Oct 1997) |
| germ-free isolator | A chamber which has absolutely no microorganisms whatsoever living in it, where a germ-free animal can be born and raised. An artificial barrier surrounding a living facility for germ-free animals, which keeps out all microorganisms. (09 Oct 1997) |
| germ-free life | Animals not contaminated by or associated with any foreign organisms. (12 Dec 1998) |
| carrier-free | A substance in which a radioactive or other tagged atom is found in every molecule; the highest possible specific activity. (05 Mar 2000) |