Deletions of lambda phage locating a prm mutation within the rightward operator.

Two deletion-substitution mutations of phage lambda, spi-113 and spi-274, are shown to remove about half of the rightward operator OR. Physiological studies show that spi-113 is still repressible. Thus, the 50 or so nucleotides of OR deleted in this mutant are not absolutely essential for repression. prm-116, which inactivates the promoter essential for the maintenance of lambda repressor synthesis, is located within OR between the endpoints of spi-113 and spi-274.