ABSTRACT
Having established that the primary control of eukaryotic gene expression lies at the level of transcription, it is necessary to investigate the mechanisms responsible for this effect. The fact that regulation at transcription is also responsible for the control of gene expression in bacteria suggests that insights into these procedures obtained in these much simpler organisms (for a review see Travers, 1993) may be applicable to higher organisms. It is possible therefore that regulation of transcription in eukaryotes might occur by means of a protein, present in all tissues, which binds to the promoter region of a particular gene and prevents its expression. In one particular cell type, or in response to a particular signal such as heat shock, this protein would be inactivated either directly (Fig. 6.1a) or by binding of another factor (Fig. 6.1b), and would no longer bind to the gene. Hence transcription would occur only in the one cell type or in response to the signal. This mechanism is based on that regulating the
expression in the bacterium E. coli of the lac operon containing the genes encoding proteins required for the metabolism of lactose. This operon is normally repressed by the lac repressor protein; binding of lactose to this protein, however, results in its inactivation and allows transcription of the operon (for a review see Muller-Hill, 1996).
