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

Abstract

PBSX and skin are two unusual genetic elements resident on the Bacillus subfilis chromosome. PBSX is a phage-li ke element located a t approximately 100" which is induced by the SOS response and results in cell lysis with the release of phage-like particles. The phage particles contain bacterial chromosomal DNA and kill sensitive bacteria without injecting DNA. The skin element is located at approximately 230" on the chromosome and is positioned within the sigK open reading frame (ORF). It is excised at a particular stage of sporulation, leading to reconstitution of the complete sigK gene. In this paper, w e show that there are phage-like operons present in the skin element which are highly homologous to the region of PBSX comprising part of the control region and the late operon. These operons are similar in terms of their gene organization, the percentage identity of the products of homologous ORFs and the positioning and strengths of ribosome-binding sites for each ORF. Although this high degree of conservation suggests that the phage-like operons in skin can be expressed, expression of the late operon was not detected during exponential growth, during sporulation or after induction of the SOS response. However two non-phage-like operons in the skin element are expressed and have distinct expression profiles that are dependent on the growth and developmental status of the cell.

The Global Transcriptional Response ofBacillus subtilisto Peroxide Stress Is Coordinated by Three Transcription Factors

“…The perR mutant strain also had significantly decreased expression of many genes, including the B regulon genes (Fig. 5), several genes of the Fur regulon (ykuNO, yxeB, ywbL, and ywbN) (1), and the PBSX defective prophage (24). While the origins of the latter effect are unclear, PBSX is known to be induced by 100 M H 2 O 2 (12).…”

Systematic sequencing of the 283 kb 210 -232 region of the Bacillus subtilis genome containing the skin element and many sporulation genes

“…2 Krogh et al, 1996). Several ORF products in the skin element also have significant similarities to those of the B. s~btilis temperate phage $105 and their arrangement is also similar ( Table 2).…”

Bacterial Genome Instability

“…This excision is nonreversible, but these specialized cells (mother cells or heterocysts) cannot divide, so the loss of DNA does not affect another generation. Interestingly, these inserted elements seem to have a phage origin (416,419). Their mechanism of action is reminiscent of the response of a lysogenic lambda phage when its host is under threat, which is to enter a lytic cycle by excising its DNA from the host chromosome (414).…”