Reporter gene is a coding unit whose product is easily assayed (such as chloramphenicol transacetylase); it may be connected to any promoter of interest so that expression of the gene can be used to assay promoter function.
Repression is the ability of bacteria to prevent synthesis of certain enzymes when their products are present; more generally, refers to inhibition of transcription (or translation) by bhinding of repressor protein to a specific site on DNA (or mRNA).
Repressor protein binds to operator on DNA or RNA to prevnt transcription or translation, respectively.
Resolvase is enzyme activity involved in sitespecific recombination between two transposons present as direct repeats in a cointegrate structure.
Restriction enzymes recognize specific short sequences of (usually) unmethylated DNA and cleave the duplex (sometimes at target site, sometimes elsewhere, depending on type).
Restriction fragment length poymorphism (RFLP) refers to inherited differences in sites for restriction enzymes (for example, caused by base changes in the target site) that result in differences in the lengths of the fragments produced by cleavage with the relevant restriction enzyme. RFLPs are used for genetic mapping to link the genome directly to a converntional genetic marker.
Restriction map is a linear array of sites on DNA cleaved by various restriction enzymes.
Retroposon is a transposon that mobilizes via an RNA form; the DNA element is transcribed into RNA, and then reverse-transcribed into DNA, which is inserted at a new site in the genome.
Retroregulation describes the ability of a sequence downstream to regulate translation of an mRNA.
Retrovirus is an RNA virus that propagates via conversion into duplex DNA.
Reverse transcription is synthesis of DNA on a template of RNA; accomplished by reverse transcriptase enzyme.
Reverse translation is a technique for isolating genes (or mRNAs ) by their ability to bybridize with a short oligonucleotide sequence prepared by predicting the nucleic acid sequence from the known protin sequence.
Reversion of mutation is a change in DNA that either reverses the original alteration (true reversion) or compensates for it (second site reversion in the same gene).
Revertants are derived by reversion of a mutant cell or orgaism.
Rho factor is a protein involved in assisting E. coli RNA polymerase to terminate transcription at certain (rho-dependedt) sites.
Rho-independent terminators are sequences of DNA that cause E. coli RNA polymerase to terminate in vitro in the absence of rho factor.
Rifamycins (including rifampicin) inhibit transcription in bacteria.
Right splicing junction is the boundary between the right end of an intron and the left end of the adjacent exon.
RNAase is an enzyme whose substrate is RNA.
RNA-driven hybridization reactions use an excess of RNA to react with all complementary sequences in a single-stranded preparation of DNA.
RNA polymerase is an enzyme that synthesizes RNA using a DNA template (formally described as DNA-dependent RNA polymerase).
RNA replicase is an enzyme that synthesizes RNA using an RNA template (used for replication by RNA viruses).
Rolling circle is a mode of replication in which a replication fork proceeds around a circular template for an indefinite number of revolutions; ;the DNA strand newly synthesized in each revolution displaces the strand synthesized in the previous revolution, giving a tail containing a linear series of sequences complementary toe the circular template strand.
Rot is the product of RNA concentration and time of incubation in an RNA-driven hybridization reaction.
Rought ER consists of endoplasmic reticulum associated with rigosomes.

S phase is the restricted part of the eukaryotic cell cycle during which synthesis of DNA occurs.
S1 nuclease is an enzyme that specifically degrades unpaired (single-stranded) sequences of DNA.
Saltatory replication is a sudden lateral amplification to produce a large number of copies of some sequence.
Satellite DNA contsists of many tandem repeats (identical or related) of a short basic repeating unit.
Saturation desity is the density to which cultured eukaryotic cells grow in vitro before division is inhibited by cell-cell contacts.
Saturation bybridization experiment has a large excess of one component, causing all complementary sequences in the other component to enter a duplex form.
Scaffold of a chromosome is a proteinaceous structure in the shape of a sister chromatid pair, generated when chromosomes are depleted of histones.
Scare (complex) mRNA comsists of a large number of individual mRNA species, each present in very few copies per cell.
scRNA is any one of several small cytoplasmic RNAs, molecules present in the cytoplasm and (sometimes) nucleus. scRNPs are small cytoplasmic ribonucleoprotein (scRNAs associated with proteins).
Segmentations genes are concerned with controlling the number or polarity of body segments in insects.
Selection describes the use of particular conditions to allow survival only of cells with a particular phenotype.
Semiconservative replication is accomplished by separation of the strands of a parental duplex each then acting as a template for synthesis of a complementary strand.
Semidiscontinuous replication is mode in which one new strand is synthesized continuously while the other is synthesized discontinuously.
Sepum constitutes the material that forms in the center of a bacterium to divide it into twi daughter cells at the end of a division cycle.
Serum dependence describes the need of eukaryotic cells for factors contained in serum in order to grow in culture.
Sex chromosomes are those whose contents are different in the two sexes; usually labeled X and Y (or W and Z), one sex has XX (or WW), the other sex has YX (or WZ).
Sex linkage is pattern of inheritance shown by genes carried on a sex chromosome (usually the X).
Sex plasmid is actually an episome; it is able to intitiate the process of conjugation, by which chromosomal material is transferred from one bacterium to another.
Shine-Dalgarno sequence is part or all of the polypurine sequence AGGAGG located on bacterial mRNA just prior to an AUG initiation condon; is complementary to the sequence at the 3’ end of 16S rRNA; involved in binding of rigosome to mRNA.
Short-period interspersion is a parttern in a genome in which moderately repetitive DNA sequences of ～300 bp alternate with nonrepetitive sequences of ～1000bp.
Shotgun experiment is cloning of an entire genome in the form of randomly generated fragments.
Shuttle vector is a plamid construdcted to have origins for replication for two hosts (for example, E. coli and S. cerevisiae) so that it can be used to carry a foreign sequence in either prokaryotes or eukaryotes.
Sigma factor is the subunit of bacterial RNA polymerase needed for initiation; is the major influence on selection of binding sites (promoters).
Signal hypothesis describes the role of the N-termainal sequence of a secreted protein in attaching nascent polypeptide to membrane; that is, mRNA and ribosome are attached to membrne via the N-terminal end of the protein under synthesis.
Signal sequence is the region of a protein (usually N-termainal) responsible for co-translational insertion into membranes of the endoplasmic reticulum.
Signal transduction describes the process by which a receptor interacts with a ligand at the surface of the cell and then transmits a signal to trigger a pathway within the cell.
Silent muations do not change the product of a gene.
Silent sites in a gene describe those positions at which mutations do not alter the product.
Simple-sequence DNA equals satellite DNA.
SINES are a class of retroposons found as short interspersed repeats in mammalian genomes; derived form transcripts of RNA polymerase III.
Single-copy plasmids are maintained in bacteria at a ratio of one plasmid for very host chromosome.
Single-strand assimilation describes the ability of Rec A protein to cause a single strand of DNA to displace its homologous strand in a duplex; that is the single strand is assimilated into the duplex.
Single-strand exchange is a reaction in which one of the strands of a duplex of DNA leaves its former partner and instead pairs with the complementary strand in another molecule, displacing its homologue in the second duplex.
Sister chromatids are the copies of a chromosome produced by its replication.
Site-specific recombination occurs between two specific (not necessarily homologous) sequences. as in phage integration/excision or resolution of cointegrate structures during transposition.
Slow component of a reassociation reaction is the last to reassociate; usually consists of nonrepetivive DNA.
Slow-stop dna mutants of E. coli complete the current round of bacterial replication but cannot initiate another at 42℃.
Smooth ER consists of a regions of endoplasmic reticulum devoid of ribosomes.
snRNA (small nuclear RNA) is any one of many small RNA species confined to the nucleus; several of the snRNAs are involved in splicing or other RNA processing reactions.
snRNPs are small nuclear ribonucleoproteins (snRNAs associated with proteins).
Solution hybridization is the same as liquid hybridization.
Somatic cells are all the cells of an organism except those of the germ line.
Somatic mutation is a mutation occurring in a somatic cell, and therefore affecting only its descendants; it is not inherited.
SOS box is the DNA sequence (operator) of ～20 bp recognized by LexA repressor protein.