THE PHAGE-LIKE ELEMENT PBSX AND PART OF THE SKIN ELEMENT, WHICH ARE RESIDENT AT DIFFERENT LOCATIONS ON THE BACILLUS-SUBTILIS CHROMOSOME, ARE HIGHLY HOMOLOGOUS

PBSX and skin are two unusual genetic elements resident on the Bacillu s subtilis chromosome. PBSX is a phage-like element located at approxi mately 100 degrees which is induced by the SOS response and results in cell lysis with the release of phage-like particles. The phage partic les contain bacterial chromosomal DNA and kill sensitive bacteria with out injecting DNA. The skin element is located at approximately 230 de grees on the chromosome and is positioned within the sigK open reading frame (ORF). It is excised at a particular stage of sporulation, lead ing to reconstitution of the complete sigK gene. In this paper, we sho w that there are phage-like operons present in the skin element which are highly homologous to the region of PBSX comprising part of the con trol region and the late operon. These operons are similar in terms of their gene organization, the percentage identity of the products of h omologous ORFs and the positioning and strengths of ribosome-binding s ites for each ORF. Although this high degree of conservation suggests that the phage-like operons in skin can be expressed, expression of th e late operon was not detected during exponential growth, during sporu lation or after induction of the SOS response. However two non-phage-l ike operons in the skin element are expressed and have distinct expres sion profiles that are dependent on the growth and developmental statu s of the cell.