The effect of virL mutation on the gene expression was studied. λvirL mutant expresses the N gene function but not the 0 gene function as analysed by the method of hetero-immune phage complementation in the presence of λ repressor. The λ specific exonuclease which is induced by the N gene product was produced by λvirL in λcIts lysogen. VirL region may be an operator region of the left-hand operon.
