Cells have evolved multiple strategies to adapt the composition and
quality of their protein equipment to needs imposed by changes in intra-
and extracellular conditions. The appearance of pro teins transmit- ting
novel functional properties to cells can be controlled at a transcrip-
tional, posttranscriptional, translational or posttranslational level.
Extensive research over the past 15 years has shown that transcriptional
regulation is used as the predominant strategy to control the production
of new proteins in response to extracellular stimuli. At the level of
gene transcription, the initiation ofmRNA synthesis is used most
frequently to govern gene expression. The key elements controlling
transcription initiation in eukaryotes are activator proteins
(transactivators) that bind in a sequence-specific manner to short DNA
sequences in the of genes. The activator binding sites are elements of
larger proximity control units, ca lied promoters and enhancers, which
bind many distinct proteins. These may synergize or negatively cooperate
with the activators. The do novo binding of an activator to DNA or, if
already bound to DNA, its functional activation is what ultimately turns
on a high-level expression of genes. The activity of transactivators is
controlled by signalling pathways and, in some cases, transactivators
actively partici- pate in signal transduction by moving from the
cytoplasm into the nuc1eus. In this first volume of Inducible Gene
Expression, leading scientists in the field review six eukaryotic
transactivators that allow cells to respond to various extracellular
stimuli by the expression of new proteins.
