IN BACILLUS-SUBTILIS-168, TEICHOIC-ACID OF THE CROSS-WALL MAY BE DIFFERENT FROM THAT OF THE CYLINDER - A HYPOTHESIS BASED ON TRANSCRIPTION ANALYSIS OF TAG GENES

Five of the genes known to encode the enzymes for the synthesis of pol y(glycerol phosphate), the major teichoic acid of Bacillus subtilis 16 8, are organized in two divergently transcribed operons, tagAB and tag DEF. lacZ and gus transcriptional fusions to the first genes of these operons revealed that: (i) in media of different richness, higher grow th rates were paralleled by lower transcription revels; (ii) upon tran sition to stationary phase, the transcription per unit mass of both op erons increased abruptly by a factor of about two; and (iii) a rise in temperature was accompanied by decreased transcription of tagA and in creased transcription of tagD. Mapping of transcription start points r evealed two divergent sigma(A)-controlled promoters. Although tagD and the neighbouring downstream gene tagE are transcribed from the same p romoter, the Tatter was expressed at a much lower level than the forme r. Moreover, expression of tagE, and of the translationally coupled ta gF, did not increase at the onset of the stationary phase, indicating that additional regulatory signals may act in the intergenic tagD-tagE region. Optimal transcription of these operons appears to require the entire regulatory region, suggesting that tag gene expression may, am ong other factors, be regulated by the three-dimensional configuration of this segment. The biological implications of these results are dis cussed.