Control of transcription of the repressor gene in bacteriophage lambda

The rate of transcription of the structural gene for repressor (cI gene) in bacteriophage lambda is controlled by the amount of active repressor in the cell. When the (reversibly) thermolabile repressor in a bacterium lysogenic for lambdacI(857) is inactivated by heat, the rate of repressor gene transcription immediately falls. If the repressor is renatured, synthesis of repressor messenger is immediately restored to a high rate. Control by the repressor of the rate of transcription of its own structural gene does not depend upon the expression of any other known gene because the control can be observed in an N(-)x(-)lysogen.Measurement of lambda repressor gene transcription was made possible by a two-step hybridization technique utilizing prehybridization to lambdadv plasmid DNA. Application of this technique also showed that the product of the N gene stimulates transcription of the r strand in the region of the cII, O, and P genes.