Page 52 - Academic Press Encyclopedia of Physical Science and Technology 3rd Molecular Biology

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Encyclopedia of Physical Science and Technology EN006H-655 June 29, 2001 21:21

Gene Expression, Regulation of

G¨oran Akusj¨arvi
Uppsala University

I. Introduction
II. Definition of a Transcription Unit
III. Regulation of Transcription in Eukaryotes
IV. Regulation of Transcription in Prokaryotes
V. Posttranscriptional Regulation of Gene
Expression

GLOSSARY removed from the precursor-RNA before the mature
mRNA,rRNA,ortRNAistransportedtothecytoplasm.
Exon In eukaryotes, the part of the precursor-RNA that UsnRNP AnRNAproteincomplexconsistingofuridine-
reaches the cytoplasm as part of a mRNA, rRNA, or rich small nuclear RNAs (U snRNAs) complexed with
tRNA (see also intron). a common set of proteins, the Sm proteins, and U
Intron The part of the precursor-RNA that is removed snRNA-specific proteins. The U1, U2, U4, U5, and U6
during RNA splicing, before the mature mRNA, rRNA, snRNPs are involved in RNA splicing. Other U snRNPs
or tRNA is transported to the cytoplasm (see also serve other functions in the cell.
exon).
Nucleosome The basic structural unit used to condense
DNA in a cell. The nucleosome consists of a disc- OUR GENES are stored in a stable DNA molecule that
shaped core of histone proteins (H2A, H2B, H3, and is faithfully replicated and transmitted to new daughter
H4) around which an approximately 146-base-pair seg- cells. Each cell in our body contains the same genetic
ment of DNA is wrapped. information. The development of complex multicellular
Precursor-RNA The nuclear RNA transcript produced organisms such as humans with highly specialized organs
by transcription of the DNA. The precursor-RNA con- and cell types then arises through a complex regulation
tains both exonic and intronic sequences. Introns are of expression of the genetic material. Recent advances in
removed by RNA splicing before the mature RNA is whole-genome sequencing have suggested that the differ-
transported to the cytoplasm. ence between a simple organism like a bacteria and a much
Promoter The DNA sequence element that determines morecomplexorganismlikeahumanmayonlyresultfrom
the site for transcription inititation for an RNA poly- as little as a 5- to 10-fold difference in the number of genes.
merase. Thus, a prototypical bacterial genome encodes for 2000–
RNA splicing The nuclear process by which introns are 4000 genes, whereas the recently completed sequencing of

501