CHAPTER 6 - Regulation of Gene Expression in Mammalian Cells

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This chapter focuses on the regulation of gene expression in mammalian cells. In mammalian tissues, in fact in most eukaryotic tissues, a recognized predominant action of cyclic AMP (cAMP) is the stimulation of enzymic phosphokinase activities that are responsible for the phosphorylation of proteins. It has been proposed that hormones that activate adenyl cyclase regulate gene activity via the cAMP promotion of histone phosphorylation, the latter permitting more efficient gene transcription than does its non-phosphorylated form. Many attempts have been made to demonstrate that hormones exert their effects on gene expression at the level of gene transcription, analogous to the action of inducers on the lactose operon in Escherichia coli. An integral part of the regulatory mechanisms in prokaryotes is the rapid turnover of messenger RNA molecules. Thus, when specific gene transcription is repressed, the concentration of specific RNA template rapidly falls and the synthesis of the specific protein ceases. Furthermore, the rate of specific protein synthesis is frequently determined only by the concentration of specific template RNA. Any system in which a paradoxical stimulation of specific protein synthesis is caused by inhibitors of RNA synthesis is quite likely to be subject to a posttranscriptional regulation of gene expression. Therefore, it may be that the posttranscriptional regulation of gene expression is a general mechanism found in many developing and inducible systems of eukaryotes.