| LAC | La Crosse [virus]; lactase; left atrial circumflex [artery]; left atrial contraction; linguoaxiocerv... |
|---|---|
| LaC | labiocervical |
| lac | laceration; lactation |
| DABP | D site albumin promoter binding protein |
| ESP | early systolic paradox; echo spacing; effective sensory projection; effective systolic pressure; end... |
| Lac | L(+)-lactate |
|---|---|
| LAC | La Crosse |
| LacO | Lac operator |
| Lac | Lactose |
| LAC | Los Angeles County |
| seed-lac | A species of lac. See the Note under Lac. Source: Websters Dictionary (01 Mar 1998) |
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| lac | A resinous substance produced mainly on the banyan tree, but to some extent on other trees, by the Coccus lacca, a scale-shaped insect, the female of which fixes herself on the bark, and exudes from the margin of her body this resinous substance. Stick-lac is the substance in its natural state, incrusting small twigs. When broken off, and the colouring matter partly removed, the granular residuum is called seed-lac. When melted, and reduced to a thin crust, it is called shell-lac or shellac. Lac is an important ingredient in sealing wax, dyes, varnishes, and lacquers. Ceylon lac, a resinous exudation of the tree Croton lacciferum, resembling lac. Lac dye, a scarlet dye obtained from stick-lac. Lac lake, the colouring matter of lac dye when precipitated from its solutions by alum. Mexican lac, an exudation of the tree Croton Draco. Origin: Per. Lak; akin to Skr. Laksha: cf. F. Lague, It. & NL. Lacca. Cf. Lake a colour, Lacquer, Litmus. Source: Websters Dictionary (01 Mar 1998) |
| Lac operon | Group of adjacent and coordinately controlled genes concerned with the metabolism of lactose in E. Coli. The lac operon was the first example of a group of genes under the control of an operator region to which a lactose repressor binds. When the bacteria are transferred to lactose containing medium, allolactose (which forms by transglycosylation when lactose is present in the cell) binds to the repressor, inhibits the binding of the repressor to the operator and allows transcription of mRNA for enzymes involved in galactose metabolism and transport across the membrane (_ galactosidase, galactoside permease and thiogalactoside transacetylase). (18 Nov 1997) |
| lac sulfuris | Sublimed sulfur boiled with lime water, the lime being removed from the precipitate by washing with diluted hydrochloric acid; used in preparing sulfur ointment and in the treatment of various skin disorders. Synonym: lac sulfuris, milk of sulfur. (05 Mar 2000) |
| lac vaccinum | Cow's milk. (05 Mar 2000) |
| constituative promoter | An unregulated promoter that allows for continual transcription of itsassociated gene. (09 Oct 1997) |
| promoter | <molecular biology> A region of DNA to which RNA polymerase binds before initiating the transcription of DNA into RNA. The nucleotide at which transcription starts is designated +1 and nucleotides are numbered from this with negative numbers indicating upstream nucleotides and positive downstream nucleotides. most bacterial promoters contain two consensus sequences that seem to be essential for the binding of the polymerase. The first, the Pribnow box, is at about 10 and has the consensus sequence 5' TATAAT 3'. The second, the 35 sequence, is centred about 35 and has the consensus sequence 5' TTGACA 3'. most factors that regulate gene transcription do so by binding at or near the promoter and affecting the initiation of transcription. Much less is known about eukaryote promoters, each of the three RNA polymerases has a different promoter. RNA polymerase I recognises a single promoter for the precursor of rRNA. RNA polymerase II, that transcribes all genes coding for polypeptides, recognises many thousands of promoters. most have the Goldberg Hogness or TATA box that is centred around position 25 and has the consensus sequence 5' TATAAAA 3'. Several promoters have a CAAT box around 90 with the consensus sequence 5' GGCCAATCT 3'. There is increasing evidence that all promoters for housekeeping genes contain multiple copies of a GC rich element that includes the sequence 5' GGGCGG 3'. Transcription by polymerase II is also affected by more distant elements known as enhancers. RNA polymerase III synthesises 5s ribosomal RNA, all tRNAs and a number of small RNAs. The promoter for RNA polymerase III is located within the gene either as a single sequence, as in the 5s RNA gene or as two blocks, as in all tRNA genes. (13 Nov 1997) |
| promoter insertion | <molecular biology> Activation of a gene by the nearby integration of a virus. The long-terminal repeat acts as a promoter for the host gene. A form of insertional mutagenesis. (18 Nov 1997) |
| promoter regions | <genetics> DNA sequences which are recognised (directly or indirectly) and bound by a DNA-dependent RNA polymerase during the initiation of transcription. Highly conserved sequences within the promoter include the pribnow box in bacteria and the tata box in eukaryotes. (12 Dec 1998) |
| down promoter mutation | <molecular biology> A mutation (a change in base pair sequence) in a promoter region, this results in lower gene expression (less transcription of the gene occurs). (09 Oct 1997) |
| tumour promoter | <molecular biology, oncology> Agent that in classical studies of carcinogenesis in rodent skin was able to increase the sensitivity of tumour formation by a previously applied primary carcinogen, but was unable to induce tumours when used alone. Important example was croton oil, active ingredients of which are now believed to be phorbol esters. These are believed to act as analogues of diacylglycerols and may activate protein kinase C. Strictly speaking, not the same as a co carcinogen, which is defined as being active when administered at the same time. Tumour promoters generally are carcinogens when tested more stringently. (18 Nov 1997) |
| up promoter mutation | A mutation that increases the frequency of initiation of transcription. (05 Mar 2000) |
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