The DNA enzymology of protein machines.

When I was asked to prepare this introduction, I very nearly declined. Being not nearly as wise as Alan Campbell, I knew that I could not attempt to match his scholarly introduction to the 1980 Cold Spring Harbor Symposium, the last Symposium to deal with these issues. Also, unlike him, my own contributions to the area of genetic recombination have been quite modest. I completely missed out on the two most striking enzymological discoveries in the genetic recombination field: in vitro, site-specific genetic recombination catalyzed by the X integrase protein (Nash 1981), and the synapsis step of general recombination catalyzed by the Escherichia coil RecA protein (Radding 1982). Moreover, although I am a supposed expert in DNA replication, it took me a long time to realize the general significance of the seminal finding made by Ahmad Bukhari here at Cold Spring Harbor that the transposition of bacteriophage Mu involves a site-specific DNA replication process (Ljungquist and Bukhari 1977). As discussed in one of the most exciting talks given at this Symposium, Bukhari's pioneering work has now reached its logical conclusion with the reconstruction of the Mu transposition process in vitro (Mizuuchi et al., this volume). It is therefore especially fitting that this 49th Cold Spring Harbor Symposium is dedicated to his memory. My own laboratory has spent a great deal of time characterizing the DNA replication apparatus of bacteriophage T4. As most scientists over 40 years old will remember, T4 is a large bacteriophage, and its genes seem to encode all of its own DNA replication and genetic recombination proteins. Over the past 18 years, I have received a general education in DNA enzymology from our continuing struggles with this system. I agreed to accept the challenge of preparing this introduction because I believe that some of the lessons we have learned will be helpful to others struggling with the enzymology of less well understood genetic systems. Thus, I deal here with general issues rather than with details.