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- Radioactive suicide
- The death of cells due to incorporation of a radioactive substrate with high specific activity. Radioactive suicide can be used as a technique to select for mutants that are unable to incorporate a particular substrate.
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- Random primers
- A set of short oligonucleotides with variable sequences. Within a population of random oligonucleotides, some will anneal to complementary sequences in a DNA or RNA template. Use of random primers to initiate DNA synthesis in the presence of a radiolabelled (or chemiluminescent) dexoynucleotide (dNTP) will yield probes representing the sequences found in the template DNA. The labeled probes can then be used to identify other sequences homologous to this DNA (e.g. by Southern blotting).
Reading
frame
The way a sequence of nucleotides that code for a polypeptide are read as consecutive triplets.
The selection of one of three
possible ways of translating groups of three consecutive nucleotides ( codons)
in mRNA. The reading frame is determined by the initiation codon and for
any sequence of duplex DNA there are six possible reading frames.
- Read-through
- Failure to stop transcription at a normal termination signal.
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- RecA protein
- The protein encoded by the recA gene which is essential for homologous recombination. The RecA protein is also involved in the induction of the SOS response and the induction of lambda prophage in response to DNA damaging agents.
- Recessive
- A genetic trait that is not expressed in a heterozygous or partially heterozygous cell.
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- Reciprocal crosses
- Pairs of genetic crosses which in one case DNA from strain
1 is transferred into strain 2 and in the second case strain 2 is used as a donor to transfer the same region into strain
1. For example
Cross A = donor (pro::Tn10) x recipient (pro+)
Cross B = donor (pro+) x recipient (pro::Tn10)
- Reciprocal recombination
- A precise exchange of genetic information like that expected for a simple cut, exchange, and rejoin mechanism. That is, a region of DNA simply moves from the donor molecule to the recipient molecule in exchange for the identical region from the recipient molecule.
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- Recombinant DNA
- A molecule of DNA in which a DNA fragment from a different source has been inserted.
- Recombinase
- An enzyme that catalyzes genetic recombination.
- Recombination
- Genetic exchange resulting from a cross-over between two different DNA molecules or different regions of a DNA molecule. See General recombination, Illegitimate recombination and
Site-specific recombination.
- Recombination frequency
- The number of recombinants divided by the total number of progeny. The recombination frequency is proportional to the physical distance between two genetic markers, and thus recombination frequencies can be used to draw genetic maps showing the relative distance between genetic markers. Note that often the coinheritance frequency -- the
probability that recombination did NOT occur between two markers is used instead of the recombination frequency.
- Redundant
- Multiple copies of a gene or different genes with the same function.
- Regulon
- A group of genes or operons located at different positions on the chromosome but respond to a common regulatory protein.
- Release factors (RF)
- Proteins that facilitate the termination of translation. Translation termination occurs when a ribosome encounters one of the three stop codons (UAA, UAG, or UGA). These codons are not recognized by a tRNA but by protein release factors. RF-1 recognizes UAA and UAG, RF-2 recognizes UAA and UGA. RF-3 stimulates the activity of RF-1 and RF-2. Interaction of the RF with a stop codon causes the peptidyl transferase activity of the ribosome to catalyze the hydrolysis of the ester bond between the tRNA and
the polypeptide chain, releasing the polypeptide chain and resulting in dissociation of the ribosome.
- Replica plating
- A technique for transferring an identical pattern of bacterial colonies from one
Petri plate (the master plate) to a series of other plates containing different media. A plate containing bacterial colonies is pressed against a cylindrical block cove
red with velveteen, resulting in the transfer of many of the bacteria from each colony onto the corresponding position on the velveteen. Then a series of sterile plates are sequentially pressed against the velveteen to transfer cells from the velveteen to
the corresponding position on each Petri plate. After incubation, if the cells can grow on the particular medium in a plate colonies will appear at identical positions on each plate. Typically about 10 replica plates can be made from each master plate with about 200 isolated colonies on the master plate. Thus, it is possible to quickly screen a large number of colonies for a variety of phenotypic characteristics.
- Replication
- The process of duplicating a DNA molecule.
- Replication fork
- The region on a replicating double-stranded DNA molecule where synthesis of new DNA is taking place. The replicating fork produces a
Y-shaped region in the DNA molecule where the two strands have separated and replication is taking place.
- Replicative transposition
- The insertion of a transposable element at a new location without loss from the original location.
- Replicon
- A DNA molecule that is able to initiate its own replication. A replicon must have an origin of replication and usually also has the necessary regulatory information required for the proper initiation of DNA replication.
- Replicon fusion
- The integration of one replicon into another to form a single replicon. May occur by recombination between homologous regions of two replicons or by formation of a cointegrate during transposition of a transposable element located on one of the replicons.
- Repression
- Switching off the expression of a gene or a group of genes in response to a chemical or other stimulus.
- Repressor
- Usually refers to a DNA-binding protein that inhibits transcription under certain conditions. Transcriptional repressors typically decrease the transcription of certain other genes by specifically binding to operator sites -- one or more short DNA sequences located upstream of the structural gene. Regulation of repression is usually modulated by a ligand which binds to the repressor protein and alters its DNA-binding properties. DNA-binding may be increased by association with a co-repressor or DNA-binding may be decreased by association with an inducer.
- Resistance transfer factor (RTF)
- The component of an R-plasmid that encodes the ability to conjugate and to transfer DNA.
- Resolvase
- An enzyme which resolves a co-integrate molecule into its two component replicons.
- Restriction
- The cleavage of double-stranded DNA by an endonuclease (restriction enzyme). The restriction enzyme distinguishes between self and foreign DNA based upon the modification of its DNA-binding site (for example, by methylation).
- Restriction analysis
- Determination of the number and sizes of the DNA fragments produced when a particular DNA molecule is cut with a particular restriction endonuclease.
- Restriction endonuclease
- An endonuclease cuts double-stranded DNA by binding to specific sites, in many cases arranged in palindromes. Several different classes of restriction endonucleases can be differentiated based upon their binding and cleavage sites and their required
cofactors. Although restriction endonucleases have specific recognition sites, cleavage may occur at specific or random sites depending on the class of the endonuclease. Also called restriction enzymes.
- Restriction fragment length polymorphism (RFLP)
- A mutation that results in a detectable change in the pattern of fragments obtained when a DNA molecule is cut with a restriction endonuclease.
- Restriction map
- A map showing the positions of different restriction sites in a DNA molecule.
- Restrictive conditions
- The particular environmental conditions which do not allow growth of a conditional lethal mutant but result in the expression of the mutant phenotype.
- Reversion
- Any mutation that restores the wild-type phenotype of a mutant.
- R-factor
- A transmissible plasmid that carries genes
coding for resistance to several different antibiotics. Also called
R-plasmid.
- RFLP
- See Restriction fragment length polymorphism.
- Rho factor
- A protein which catalyzes transcription termination at certain sites or when an extended stretch on nontranslated, unstructured RNA is present. See Polar
mutation.
- Ribosomal (rRNA)
- An RNA molecule that forms part of the structure of a ribosome.
- Ribosome
- An RNA-protein complex responsible for the correct positioning of mRNA and charged tRNAs allowing proper alignment of amino acids during protein synthesis.
- Ribosome binding site
- A short nucleotide sequence upstream of a gene which forms the site on the mRNA molecule where the ribosome binds. (Also called a Shine-Delgarno sequence.)
- Rich medium
- A growth medium in which not all the components have been identified. Most "rich" media have a variety of complex, undefined
components.
- rII locus
- A region from phage T4 that determines whether this phage can grow on E. coli K or B strains. Fine structure genetic mapping of the rII locus by S. Benzer first unveiled a variety of important facets of gene structure and function.
- RNA phage
- A phage that carries RNA as its genetic material. Some examples include phage MS2 and Qß.
- RNA polymerase (DNA-dependent)
- An enzyme responsible for the synthesis of RNA from its constituent ribonucleotides (NTPs), using one strand of DNA as template.
- Rolling circle (sigma) replication
- A type of DNA replication where a replication fork moves around a circular DNA molecule, producing a
single-stranded concatamer (much like the way toilet paper peels off the roll). The resulting
single-stranded DNA may become double-stranded by the synthesis of a complementary strand.
- RNase
- An enzyme that hydrolyses RNA molecules.
- rpm
- Revolutions per minute.
