Abstract
The circular, single-stranded DNA genome of the Pf3 bacteriophage was sequenced in its entirety by each of two methods, the M13-dideoxy chain termination method and the chemical degradation method. It consists of 5,833 nucleotides. With respect to both the DNA and the protein sequences, there is virtually no homology between Pf3 and the phages Ff (M13, f1, and fd) and IKe. However, similarities between these phages were noted with respect to their overall genome organizations. The gene for the single-stranded DNA-binding protein is followed by the gene for the major coat protein and then by a transcription termination signal. Open reading frames for seven other proteins were predicted, and their sizes and order show a fair correspondence to the sizes and order of the genes of the Ff phages and IKe. In addition, several regions have the potential to form stem and loop structures similar to those in the intergenic region of the Ff phage genome, but in Pf3 some are within open reading frames. Evolutionary relationships between Pf3 and the Ff phages and IKe are thus apparent through the correspondence of overall gene order rather than through primary sequence homologies.