ADDITION OF NUCLEOTIDES TO PARENTAL DNA EARLY IN INFECTION BY BACTERIOPHAGE T4

Tritiated thymidine is incorporated into acid-insoluble material within the first five minutes after infection of Escherichia coli with bacteriophage T4, a time well before normal replication has commenced. The nature of this early-incorporated material is explored in this paper. The material, which cosediments with DNA from mature phage in sucrose gradients, is formed by wild-type T4 and by several DNA-negative amber mutants. It is phage-specific, as judged by its failure to be detected in uninfected cells, its pyrimidine base composition, and its ability to hybridize with another, well-characterized (Frankel, 1966) replicative intermediate formed later in infection. The material exists largely, but not completely, in a duplex structure. The amount of material formed per cell is dependent upon the multiplicity of infection and occurs, on an average basis, to the extent of about 8000 molecules of thymidine incorporated per parental molecule, containing about 124,000 molecules of thymidine. For this reason, and because the early material assumes the density of parental DNA in a bromouracil-labeling experiment, we believe that the early incorporation of DNA precursors represents addition of nucleotides to parental DNA molecules. The extent of addition is too small to appreciably affect the sedimentation rate under our conditions of zone centrifugation. © 1969.