Analysis of Bacillus subtilis tag gene expression using transcriptional fusions

Five of the genes known to encode the synthesis of poly(glycerol phosphate), the major teichoic acid of Bacillus subtilis 168, are organized in two divergently transcribed operons (a divergon), denoted tagAB and tagDEF. To monitor their expression, the 399 bp intergenic region separating the first structural genes of these operons was fused, in both orientations, to a lacZ reporter gene, allowing measurement of promoter activity under specific physiological conditions. Under all experimental conditions, tagA and tagD appeared coordinately expressed, the level of tagD being always higher than that of tagA. No influence of the chromosomal context was observed. Phosphate limitation was accompanied by reduced tag gene expression. Following the onset of sporulation, expression of tag genes diminished rapidly and was essentially abolished by stage II. During germination, the activity of tag genes was detectable before the rise in culture turbidity associated with spore outgrowth. In contrast to tagC (dinC), the expression of which is DNA-damage-inducible, the induction of SOS functions had no effect on tagA and tagD gene expression. The biological significance of these results is discussed.