GENETIC STRUCTURE OF BACTERIOPHAGE T4 AS DESCRIBED BY RECOMBINATION STUDIES OF FACTORS INFLUENCING PLAQUE MORPHOLOGY

Abstract

I N the study of biological replication, the most proniising methods of attack appear to involve the use of genetic specificities. For the investigation of this problem with bacteriophage, it is then important to make available a rather abundant supply of genetic markers and to learn their genetic properties. This paper deals with the hereditary characteristics of a class of previously unde-scribed genetic factors and their recombination frequencies with known r (rapid lysis) and 1% (minute) loci both of which influence plaque morphology (HERSHEY and ROTMAN 1948, 1949). The factors to be described are designated by the genetic symbol tu because they increase the turbidity of the plaque halo. Merition of some of the plaque types involved has been made previously in a brief report (DOERMANN and DISSOSWAY 1949). HERSHEY and ROTMAN'S data (1948, 1949) for the recombination frequencies among r, h (host range), and w loci in phage T 2 indicate some kind of linkage system but their data were sufficient to establish only that a linear arrangement is a possibility. The data presented in this paper indicate a linear order for at least five linked factors in one group, and three in another. MATERIALS AND METHODS Bacteriophage T 4 was used throughout these experiments except where the purpose was the introduction of two of HERSHEY and ROTMAN'S (1948) r factors into T 4 from T2. The single m factor used in T 4 was obtained by isolating a mutant from a genetically complex stock. The mutant was crossed to wild type and T4m was obtained as a segregant. The r mutants originating in T 4 were obtained by isolation of a single r from each of a number of mottled plaques. Each of these arose from an individual T4r+ particle. Similarly all the tu strains were obtained from independent mutations in T4rd8tu+. Large numbers of tu's are readily collected since a 24-hour plaque of rtu+ invariably contains a small proportion of tu mutants.