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Abstract
The RNA polymerase II core promoter is a structurally and functionally diverse transcriptional
regulatory element. There are two main strategies for transcription initiation - focused
and dispersed initiation. In focused initiation, transcription starts from a single
nucleotide or within a cluster of several nucleotides, whereas in dispersed initiation,
there are several weak transcription start sites over a broad region of about 50 to
100 nucleotides. Focused initiation is the predominant means of transcription in simpler
organisms, whereas dispersed initiation is observed in approximately two-thirds of
vertebrate genes. Regulated genes tend to have focused promoters, and constitutive
genes typically have dispersed promoters. Hence, in vertebrates, focused promoters
are used in a small but biologically important fraction of genes. The properties of
focused core promoters are dependent upon the presence or absence of sequence motifs
such as the TATA box and DPE. For example, Caudal, a key regulator of the homeotic
gene network, preferentially activates transcription from DPE- versus TATA-dependent
promoters. The basal transcription factors, which act in conjunction with the core
promoter, are another important component in the regulation of gene expression. For
instance, upon differentiation of myoblasts to myotubes, the cells undergo a switch
from a TFIID-based transcription system to a TRF3-TAF3-based system. These findings
suggest that the core promoter and basal transcription factors are important yet mostly
unexplored components in the regulation of gene expression.
Copyright 2009 Elsevier Inc. All rights reserved.