A NEW PHAGE OF BACILLUS SUBTILIS WITH INFECTIOUS DNA HAVING SEPARABLE STRANDS

A new phage (SPP1) active on Bacillus subtilis has been isolated. The DNA extracted from the phage is infectious on competent cells of B. subtilis and shows the highest efficiency of infection so far observed for B. subtilis phage DNA, namely 5 to 6 × 103 phage equivalents per plaque-forming unit. The phage genome can be extracted as a single DNA molecule having a molecular weight of 2·5 × 107. The molecular weight of phage DNA after denaturation is approximately 1·3 × 107, thus demonstrating the absence of single-strand breaks. The buoyant density of SPP1 DNA in a neutral CsCl density-gradient is 1·703 g cm-3; denatured DNA has a bimodal density distribution at neutral pH, the two bands corresponding to the separated strands; their densities are 1·713 g cm-3 and 1·725 g cm-3, respectively. The interaction of ribosomal RNA with the heavy strand strongly enhances its density and allows a large-scale preparation of the two separated strands. The isolated strands can be reannealed, yielding a good recovery of infectious activity. © 1968.