Infectious DNA from Coliphage T1

SummaryInfectious T1-DNA stored for about 20 days at 4°c in an appropriate buffer contains on average 5 single-strand breaks per phage genome without detectable loss of infectivity.T1-DNA in 0·2 M NCE-buffer thermally treated for 6 min at 100°c and rapidly cooled forms an infectious molecule of mismatched configuration probably containing short-range folded single-stranded regions, 3 single-strand breaks per phage genome, a low intrinsic viscosity of [η] = 34·5 [dl./g], and an increased sedimentation coefficient indicating a change in molecular conformation.No double-strand breaks and a negligible number of single-strand breaks are observed in unsubstituted infectious T1-DNA after inactivation with u.v.-light of 2537 Å. After incorporation of 5-bromouracil, however, single-strand breaks are produced in infectious T1-DNA at a yield of 0·9 breaks per lethal hit requiring an exposure to 45 ergs/mm2 per break. The relation of double to single-strand breaks is 1/17. The relevance of the breaks to the biological activity of infectious T1-DNA is discussed.