Construction and characterization of a cohesive end site mutant of bacteriophage λ

Abstract

A cohesive end site mutant ( cos1) of bacteriophage λ has been isolated following in vitro manipulations of λ DNA, including removal of the cohesive ends by digestion with S1 nuclease. The resulting mutation is a 0.4-kilobase deletion which starts at cos, as determined by heteroduplex studies, and extends to the right into the Nu1 gene. Mature λ chromosomes are normally generated by cleavage of two cos sites: Packaging proceeds in an A gene to R gene direction from an initial cos site to a terminal cos site. The cos1 mutation inactivates cos function at both the initial and the terminal cleavages. Aside from the Nu1 defect, expression of all the morphogenesis genes by λ cos1 is normal. Complementation experiments give results expected for a cos mutant: The cos1 mutation results in a cis-specific packaging defect.