PACKAGING OF THE BACTERIOPHAGE-LAMBDA CHROMOSOME - ROLE FOR BASE SEQUENCES OUTSIDE COS

The genetic basis for the divergent packaging specificities of phages λ and 21 (B. Hohn, 1975, J. Mol. Biol., 98, 93-106) has been examined. A hybrid derivative of lambda containing a substitution of the 21 head genes and left chromosome terminus has 21 packaging specificity, so the divergent packaging specificities of λ and 21 result from differences in this region. Helper packaging experiments show that lambda and 21 can carry out cohesive end site (cos) cleavage on chromosomes of the opposite packaging specificity, indicating that cos cleavage per se is not the reason for the divergent packaging specificities. Sequencing studies, compatible with the helper packaging studies, show that the cohesive end sites of lambda and the λ-21 hybrid are identical. It is concluded that base sequences outside of the 22 base pair cos segment are responsible for the packaging specifities of λ and 21. The possible molecular basis for the packaging specificities of λ and 21 is discussed. Complementation studies between lambda head ambers and phage 21 show that only D and FII mutants can be complemented by 21. Since DNA packaging involves specific interactions between DNA and recognition proteins and the prehead, it is not surprising that few components are interchangeable between these two systems. © 1979.