<i>Trans</i> -Acting Factors

Abstract Transcription factors are trans-acting proteins that affect the rate of transcription by specific interactions with DNA and/or other proteins (see Chapter 1). Transcriptional activators and repressors have positive and negative effects, respectively, on the rate of transcription. Transcriptional regulators may affect the rate of transcription initiation and/or mRNA elongation. In addition to DNA-binding activators and repressors, a variety of coactivators, corepressors, and other cofactors have been identified that do not bind to DNA directly but instead interact with the DNA-binding proteins and mediate their effects on transcription. Some of these co-factors have enzymatic activities that allow them to modify other cofactors, Pol II, or histones. Each of the transcription factor classes listed in Table 3.1 will be described in this chapter, followed by a discussion of pathways that transduce signals (e.g., cytokines, growth fac tors, and small molecules) at the cell surface to transcription factors that alter gene expression in the nucleus.