APPENDIX I: Spontaneous Mutations in the Escherichia coli Prophage P1 and IS-Mediated Processes

Abstract

A recent genetic and physical study (Arber et al. 1979) of spontaneous P1 prophage mutants affected in the vegetative phage propagation revealed that at the most a few percent of spontaneous mutations were caused by nucleotide substitution or other small alterations in the nucleotide sequence. About 70% of all mutations studied were relatively long deletions clustering around the single IS1 element carried in the wild-type P1 genome. The rest, about 27% of the mutants, carried an additional DNA segment most likely representing a transposable IS element from the Escherichia coli host chromosome rather than a partial duplication of phage genetic material. On the one hand, these findings point to the importance of IS elements in the production of spontaneous mutations. On the other hand, they open an interesting approach to investigate the diversity of IS elements carried in bacteria serving as hosts for bacteriophage P1.