PACKAGING OF THE BACTERIOPHAGE-LAMBDA CHROMOSOME - DEPENDENCE OF COS CLEAVAGE ON CHROMOSOME LENGTH

Packaging of the bacteriophage lambda chromosome is polarized, proceeding from an initial cohesive end site (cos) in an A to R direction to a terminal cos site. We have performed helper packaging studies which indicate that the frequency of cleavage of the terminal cos site is dependent on the length of the chromosome being packaged. The helper packaging experiments involved infection of repressed lysogens containing a packagable chromosome by a heteroimmune helper. The prophage at which packaging terminated contained a cos duplication segment, so that failure to terminate packaging by cleavage of the first cos site results in packaging of a cos duplication chromosome. The frequency of packaging of chromosomes with the duplication decreases with increasing chromosome length, leading to the conclusion that cos cleavage depends on chromosome length. This result is most compatible with DNA packaging models in which cos cleavage follows packaging. No dependence of cleavage on the length of the distal duplication segment was found, indicating that extensive one-dimensional diffusion of DNA does not occur during packaging. © 1979.