Bacteriophage λ DNA synthesized by mutants in gene N

Abstract

DNA was extracted from E. coli cells infected with N + and N − λ phage and examined by sedimentation in alkaline sucrose gradients. The profiles of the intracellular phage DNAs were very similar at early times after infection (10 min). Both superhelical DNA molecules and forms with a relative sedimentation rate of 1 to 2 times that of mature λ single strands were present at this time. At later times (90 min), however, DNA from N − infected cells remained confined to the region of the gradient corresponding to superhelical molecules, whereas the N + DNA now sedimented in the position of mature length DNA. At intermediate times (45 min), both N − and N +-infected cells contained a hitherto unrecognized form of replicating λ DNA which sedimented in alkali at 2.7 times the rate of mature length single-stranded λ DNA molecules.