Bacteria with defective rho factors suppress the effects of N mutations in bacteriophage lambda.

A prediction based on the model for N-gene function of bacteriophage lambda proposed by Roberts (1971) is confirmed by showing that a lambdaN- double mutant is able to grow in strains of E. coli with defective rho transcription termination factors. The burst sizes for lambdaN- in these strains range from 5 to 24% the burst sizes for lambdaN+ in the same strain. This low level of suppression is also evident in the levels of synthesis of the lambda exonuclease and is consistent with other evidence that the defect in the rho factors of these strains is only partial. These strains do not suppress the effects of mutations in genes O, P and Q of lambda nor in genes 30 and 43 of bacteriophage T4. The lack of suppression of lambdaQ- is significant because the Q-gene product, like the N-gene product, is believed to function as an anti-terminator of lambda transcription but at termination sites that may not require rho factor action.