Differences in susceptibility to restriction by E. coli B between various heteroduplex molecules of bacteriophage FD DNA

Abstract

Fragments of B-modified bacteriophage fd sB1^o sB2 RF DNA were prepared with the help of purified endonuclease R from Haemophilus parainfluenzae (Hpa II). These were hybridized with unmodified circular single stranded fd DNA. The resulting partial heteroduplex molecules were assayed for infectivity on competent cells of B-restricting and non restricting strains of E. coli. There of such heteroduplexes originating from neighbouring fragments on the physical map of fd RF DNA were shown to be more resistant to Eco B restriction than six others and the unmodified control. It is suggested that the three corresponding vicinal fragments contain essential parts of the Eco B recognition site on this phage DNA.