The eukaryotic mRNA transcription machinery is exceedingly complex, perhaps reflecting the requirement for response to diverse environmental and developmental signals. Some of the machinery is common to all mRNA genes and includes RNA polymerase II (Pol II) and a set of general transcription factors (GTFs) (1). Signal-specific gene expression patterns are defined by sequence-specific DNA-binding proteins (activators) that bind cognate sites in the promoter and enhancers of target genes. In most cases activators are not sufficient for stimulation of transcription. Instead, these DNA-binding proteins initiate the ordered assembly of large multiprotein complexes (the coactiva-tors), in addition to the general factors, at the promoters of target genes (2). A cursory examination of the complexes involved in signal-responsive activated transcription in a chromatin environment indicates that >100 different polypeptides are involved in the process. Many of these proteins occur in stable multiprotein complexes.
展开▼
