Correlation between intramolecular base composition heterogeneity of DNA and control of transcriptional expression in E. coli temperate phage P2

Typescript.Thesis (Ph. D.)--University of Hawaii at Manoa, 1972.Bibliography: leaves 91-96.ix, 96 l illusIntramolecular base compositional heterogeneity has been demonstrated in the DNA of the phage P2 by following the optical density of solutions at 260 nm as a function of increasing temperature. First derivative curves of the functions thus generated have been obtained for P2 DNA and the DNA of two closely related phages. Comparison of these curves reveals similarities at the high temperature (high GC) end and differences at the low temperature (low GC) end. All three of these phages can, by supplying the genes concerned with phage particle maturation, serve as helper for the defective phage P4. The strands of P2 DNA have been separated on the basis of their buoyant densities in CsCl solutions when complexed with poly UG. In vivo transcription patterns from these strands in cells infected with various P2 mutants have demonstrated that the "heavy" strand is the one predominantly transcribed, that some "light" strand transcription originates from an operon coding for proteins involved in phage head assembly (thus fuling out a "read-through" mechanism for late gene activation), and that early "light" strand transcription does not originate from DNA deleted in two mutants which is in the right half of the physical map. There is, however, some "light" strand transcription early in infection. P2 DNA has been sheared in: half and the halves separated on the basis of Hg++ binding in Cs2SO4 density gradients. Electron microscopic analysis of partially denatured molecules in these preparations have fixed them with respect to the physical map. In ~ transcription originates primarily from the right, or low GC half early in infection and then shifts to the left, or high GC half. Mutants in genes A and B, which are located in the right half of the genetic map, are defective in both DNA replication and in effecting this shift. Infection with one polar amber mutant under non-permissive conditions has demonstrated that this operon lies :in the right half of the DNA and thus helps to fix the physical map with respect to the genetic map. Two of those regions of the phage DNA which are known to be transcribed from a repressed genome, namely the prophage, appear to be of quite low GC content