Chromosomal E. coli DNA appears to be sensitive towards in vivo DNA restriction when transformed to a restrictive E. coli recipient. It is therefore concluded that transforming chromosomal donor DNA is present in a double-stranded form immediately after uptake.
Genetic analysis of E. coli transformants, obtained with UV-irradiated donor DNA under conditions that exclude photorepair, show, especially in a uvrB recipient, loss of donor DNA information compared with the situation where DNA was not subjected to UV-irradiation. Similar conclusions were arrived at after genetic analysis of transductants obtained with UV-irradiated particles of the generalized transducing phage P1. The processing in E. coli of DNA after P1 transduction is thus similar to that of transforming DNA. The observations are discussed and a possible explanation based on single-stranded DNA integration is presented in detail.