| switching site | The break point in a DNA sequence at which a gene segment unites with another gene segment, as in the production of the immunoglobulins. (05 Mar 2000) |
|---|---|
| deoxyribonucleases, type III site-specific | <enzyme> Enzyme systems composed of two subunits and requiring ATP and magnesium for endonucleolytic activity; they do not function as atpases. They exist as complexes with modification methylases of similar specificity. The systems recognise specific short DNA sequences and cleave a short distance, about 24 to 27 bases, away from the recognition sequence to give specific double-stranded fragments with terminal 5'-phosphates. Enzymes from different microorganisms with the same specificity are called isoschizomers. Registry number: EC 3.1.21.5 (12 Dec 1998) |
| deoxyribonucleases, type II site-specific | <enzyme> Enzyme systems containing a single subunit and requiring only magnesium for endonucleolytic activity. The corresponding modification methylases are separate enzymes. The systems recognise specific short DNA sequences and cleave either within, or at a short specific distance from, the recognition sequence to give specific double-stranded fragments with terminal 5'-phosphates. Enzymes from different microorganisms with the same specificity are called isoschizomers. Registry number: EC 3.1.21.4 (12 Dec 1998) |
| 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) |
| 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) |