Chapter 5 Making and Joining DNA Ends

Abstract

Reassortment of genetic characters in λ involves breakage of DNA strands and their reunion in new arrangements (Chapters 6 and 7). The formation and joining of the molecular ends of λ DNA likewise involves breakage of DNA strands and their reunion, although the outcome of these processes is not a recombinant phage. Moreover, the formation of λ DNA ends resembles those recombinations that permit λ DNA to enter and leave the bacterial chromosome; both kinds of events are site specific. Accordingly, the present discussion of how molecular ends form and join may be viewed as a preface to the following chapter about prophage integration and excision.

Present knowledge about end formation complements available knowledge about prophage integration. The structures of the molecular ends are known; the cutting agents, as well as their genetic determinants, are not. On the other hand, the agents responsible for prophage insertion and excision are known to be determined by the int and xis genes; some progress in the isolation of at least the int protein has been made. The structures of the attachment sites are unknown, although the problem of their analysis is beginning to arouse interest. Indeed, we are witness to a current preoccupation with recognition elements in nucleic acids. The base sequences recognized by proteins involved in modification, recombination, replication, repair, transcription, and translation are receiving the attention of geneticists and biochemists together.

NATURE OF THE MOLECULAR ENDS
The thermally reversible association of λ DNA molecules in vitro was first shown by Hershey...