DNA Binding Proteins and Their Roles in Controlling Tissue Specific Gene Expression and Responses to Second Messengers
Transcriptional control is extensively used by mammalian cells to modulate the level of gene expression in response to various environmental, hormonal, developmental and nutritional signals. By modulating the rate of transcription of various genes, the cell can adapt to new nutritional requirements and adverse environmental conditions. The turning on and off of specific genes allows the cell to change its phenotype, assume new functions and progress along its developmental pathway. While the biosynthesis of any RNA molecule includes several distinct steps such as initiation, elongation and termination, in almost all cases transcriptional control occurs at the initiation step. Like other eukaryotes, mammalian cells contain three different RNA polymerases, usually abbreviated as Pol I, Pol II and Pol III. Each of these RNA polymerases is assigned to transcribe a different class of RNA molecules: e.g. Pol I is responsible for transcription of the genes coding for the 28S and 18S ribosomal RNAs; Pol II transcribes protein coding genes and Pol III is used for transcription of 5S ribosomal RNA, tRNAs, and several other small RNA species such as the small nuclear RNAs (Hansen and Sharp 1987; Heintz and Roeder 1982; Manley 1983). We will limit our discussion to the control of transcription of protein coding genes by Pol II.
KeywordsEnhancer Element Glucocorticoid Responsive Element Phorbol Ester Tumor Promoter SV40 Enhancer Human Growth Hormone Gene
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