Restriction Endonucleases, Simian Virus 40, and the New Genetics

methodological developments that have opened a new approach to the analysis of chromosomes: site-specific cleavage of DNA by restriction endonucleases and electrophoretic fractionation of the resulting fragments; recombination, cloning, and amplification of DNA segments from any source; rapid methods for determining the nucleotide sequence of DNA; site-directed in vitro mutagenesis; synthesis of polydeoxynucl eotides of predetermined sequence; and the ability to introduce cloned, functioning genes into prokaryotic or eukaryotic cells. As a result of these developments even chromosomes which are largely inaccessible to classical genetic methods can now be analysed piece by piece in chemical detail. Genes and signals can be altered at pre-selected sites, and the functional effect of such alterations determined. And active, synthetic genes can be constructed in vitro by recombination or by chemical synthesis. Many investigators have contributed to the “new genetics”. Contributions from my own laboratory resulted from our studies of a model eukaryotic chromosome, that of a small mammalian tumor virus. I became interested in tumor viruses in the mid 1960’s when I was asked to give a lecture on this subject to Johns Hopkins medical students. Although I had been working with an RNA coliphage (a bacterial virus) for some years, I knew very little about animal viruses. As I reviewed the tumor virus literature, I was impressed by the fact that simple viruses had a profound and permanent effect on the growth of cells in culture or in a living animal. Here was a microcosm of regulatory mechanisms related to the development of the virus itself and to the growth of animal cells, including neoplastic cells. At least some of these mechanisms appeared approachable with the tools of molecular genetics that had been so successfully used with bacterial viruses. Of course all of this was appreciated by a number of