Abstract
It has been shown that the restriction maps of Bacillus phages M2 and Nf are identical to each other except in the region 32 to 46% from the left ends of the genomes. Furthermore, in this region, genomes of the original stock of phage M2 were heterogeneous in length. We have found that M2 has the same origin as Nf and that the heterogeniety in the region is caused by deletions of various sizes. These results were obtained by electoron microscopic observations of heteroduplex molecules between the genomes of Nf and subclones of M2, and by fine physical mapping of the heterologous regions. Finally, it has been shown that these deletions affected phage morphology but not multiplication.
