| FR | failure rate; film-screen radiograph; fasciculus retroflexus; febrile reaction; feedback regulation;... |
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| RE | radium emanation; readmission; rectal examination; reference emitter; reflux esophagitis; regional e... |
| UGF | Urinary Gonadotropin Fragment |
| B3F | band 3 cytoplasmic fragment |
| EFC | elastin fragment concentration; endogenous fecal calcium; ephemeral fever of cattle |
| restriction enzyme, endonuclease | A protein that recognises specific, short nucleotide sequences and cuts DNA at those sites. Bacteria contain over 400 such enzymes that recognise and cut over 100 different DNA sequences. See restriction enzyme cutting site. (05 Mar 2000) |
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| restriction map | <molecular biology> Map of DNA showing the position of sites recognised and cut by various restriction endonucleases. (12 Jan 1998) |
| restriction mapping | Use of restriction endonucleases to analyze and generate a physical map of genomes or genes. The nucleotide sequence determined is often then translated into an amino acid sequence, providing a means for sequencing the protein for which the gene codes, or for which the mRNA is a messenger. (12 Dec 1998) |
| restriction methylation | The enzymatic addition of methyl groups to selected adenine and cytosine residues to protect from hydrolysis by certain restriction enzymes. (05 Mar 2000) |
| restriction nuclease | <enzyme, molecular biology> Class of bacterial enzymes that cut DNA at specific sites. In bacteria their function is to destroy foreign DNA, such as that of bacteriophages (host DNA is specifically modified at these sites). Type I restriction endonucleases occur as a complex with the methylase and a polypeptide that binds to the recognition site on DNA. They are often not very specific and cut at a remote site. Type II restriction endonucleases are the classic experimental tools. They have very specific recognition and cutting sites. The recognition sites are short, 4-8 nucleotides and are usually palindromic sequences. Because both strands have the same sequence running in opposite directions the enzymes make double stranded breaks, which, if the site of cleavage is off centre, generates fragments with short single stranded tails, these can hybridise to the tails of other fragments and are called sticky ends. They are generally named according to the bacterium from which they were isolated (first letter of genus name and the first two letters of the specific name). The bacterial strain is identified next and multiple enzymes are given Roman numerals. For example the two enzymes isolated from the R strain of E. Coli are designated Eco RI and Eco RII. (10 Mar 1998) |
| restriction site | A sequence in DNA that can be recognised and cut by a specific restriction enzyme. (12 Dec 1998) |
| 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) |
| 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) |
| active length-tension curve | The relationship between active isometric tension and preload (rest length) for a contracting muscle. (05 Mar 2000) |
| arch length | The amount of space required for the permanent teeth as measured from the mesial aspect of the first molar on one side to the mesial aspect of the first molar on the opposite side, as measured through the contact points along an imaginary line of the dental arch. (05 Mar 2000) |
| arch length deficiency | The difference between the available circumference of the dental arch and that required to accommodate the succedaneous teeth in proper alignment. (05 Mar 2000) |