Radioactive
marker A radioactive atom used in the detection
of a larger molecule in which it is incorporated.
Radioimmunoassay
(RIA) A number of different, sensitive techniques for measuring
antigen or antibody titres, using radiolabelled reagents.
RAG-1 and
RAG-2 = Recombination activating genes.
Random
amplified polymorphic DNA (RAPD) analysis A PCR technique that uses
short random primers to amplify fragments that are representative of the
genome being studied and which can be used to make comparisons between
the structures of the genomes of different organisms.
Random
priming A method for DNA labeling that utilizes random DNA hexamers
which anneal to single-stranded and act as primers for complementary strand
synthesis by a suitable enzyme.
Receptor
Any protein that binds a specific extracellular signaling molecule (ligand)
that induces a cellular response. Receptors for steroid hormones, which
diffuse across the plasma membrane, are located within the cell; receptors
for water-soluble hormones (e.g., epinephrine) and peptide growth
factors, as well as lipid soluble prostaglandins, are located in the plasma
membrane with their lignad-binding domain exposed to the external medium.
Receptors for neurotransmitters, located in postsynaptic membranes, can
regulate ion flow through the cell membrane or activate other signal transduction
pathways.
Receptor
tyrosine kinases (RTKs) An important class of cell-surface receptors
whose cytosolic domain has tyrosine-specific protein kinase activity.
This activity is activated by ligand binding and leads both to receptor
autophosphorylation and to phosphorylation of target proteins. Both types
of phosphorylations activate particular intracellular signal transduction
pathways.
Recombinant
A transformed cell that contains a recombinant DNA molecules.
Recombinant
DNA molecule A DNA molecule created in the test-tube by ligating together
pieces of DNA that are not normally contiguous.
Recombinant
DNA technology All the techniques involved in the construction, study
and use of recombinant DNA molecules.
Recombinant
protein A polypeptide that is synthesized in a recombinant cell as
the result of expression of a cloned gene.
Recombination
The exchange of DNA sequences between different molecules, occurring
either naturally or as a result of DNA manipulation. This
process also takes place during the somatic rearrangements of DNA which
occur during the formation of genes encoding antibody molecules and T-cell
antigen receptors.
Recombination
activating genes (RAG-1 and RAG-2) The genes, required for recombination
of V, D and J gene segments during generation of functional antigen receptor
genes.
Reflex
arc Neural or hormonal components that mediate a reflex usually
includes receptor, afferent pathway, integrating center, efferent pathway,
and effector.
Relaxed
Refers to the non-supercoiled conformation of open-circular DNA.
Replacement
vector A λ vector designed so that insertion of new DNA is by replacement
of part of the non-essential region of the cDNA molecule.
Replica
plating A technique whereby the colonies on an agar plate are transferred
en masse to a new plate, on which the colonies grow in the same
relative positions as before.
Replicative
form of M13 The double-stranded form of the M3 DNA molecule found
within infected E.coil cells.
Reporter
gene A gene whose phenotype can be assayed in a transformed organism,
and which is used in, for example, deletion analyses of regulatory regions.
Repression
The switching off of expression of a gene or a group of genes in response
to a chemical or other stimulus.
Renin
Hormone secreted by kineys that acts as an enzyme that catalyzes splitting
off of angiotension I from angiotensinogen in plasma.
Respiration
General term for any cellular process involving the uptake of O2
coupled to production of CO2.
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 that cuts DNA molecules only at a limited
number of specific nucleotide sequences.
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.
Reticuloendothelial
system A diffuse system of phagocytic cells derived from the
bone-marrow stem cells which are associated with the connective tissue
framework of the liver, spleen, lymph nodes and other serous cavities.
An old-fashioned term, rarely used-mononuclear phagocyte system is preferred.
Retrotransposon
Type of eukaryotic mobile DNA element whose movement in the genom is mediated
by an RNA intermediate and involves a step of reverse transcription.
Retrovirus
A virus with an RNA genome, able to insert into a host chromosome,
derivatives of which have been used to clone genes in mammalian cells.
Retrovirus replicates in cells by first making a DNA copy of the RNA,
a process termed reverse transcription. This proviral DNA is inserted
into cellular chromosomal DNA, and gives rise to further genomic RNA as
well as the mRNAs for viral proteins.
Reverse
transcriptase An RNA-dependent DNA polymerase, able to synthesize
a complementary DNA molecule on a template of single-stranded RNA.
RFLP linkage
analysis A technique that uses a closely linked RFLP as a marker for
the presence of a particular allele in a DNA sample, often as a means
of screening individuals for defective genes responsible for genetic diseased.
Ribonuclease
An enzyme that degrades RNA.
Ribosome
binding site The short nucleotide sequence upstream of a gene which
after transcription forms the site on the mRNA molecule to which the ribosome
binds.
RT-PCR
A PCR technique in which the starting material is RNA. The first step
in the procedure is conversion of the RNA to cDNA with reverse transcriptase.
Ri plasmid
An Agrobacterium rhizogenes plasmid, similar to the Ti plasmid,
used to clone genes in higher plants.
RNA splicing
A process that results in removal of introns and joining of exons in RNAs.
Splicing in the pre-mRNA of higher eukaryotes occurs in large ribonucleoprotein
complexes called spliceosomes.
Rosetting
A technique for identifying or isolating cells by mixing them with particles
or cells to which they bind (e.g. sheep erythrocytes to human T cells).
The rosettes consist of a central cell surrounded by bound cells.