ABSTRACTThe duplicatedhasRandhasLgenes ofStreptomyces ambofaciensencode alternative sigma factors (named σBRand σBL) belonging to the σBgeneral stress response family inBacillus subtilis. The duplication appears to be the result of a recent event that occurred specifically inS. ambofaciens. The two genes are 98% identical, and their deduced protein products exhibit 97% identity at the amino acid level. In contrast with the coding sequences, their genetic environments and their transcriptional control are strongly divergent. WhilehasLis monocistronic,hasRis arranged in a polycistronic unit with two upstream open reading frames,arsRandprsR, that encode putative anti-anti-σ and anti-σ factors, respectively. Transcription of eachhasgene is initiated from two promoters. In each case, one promoter was shown to be developmentally controlled and to be similar to those recognized by theB. subtilisgeneral stress response sigma factor σB. Expression from this type of promoter for each of thehasgenes dramatically increases during the course of growth in liquid or on solid media and following oxidative and osmotic stresses. Reverse transcription-PCR measurements indicate thathasRis 100 times more strongly expressed thanhasLfrom the σB-like promoter. Transcription from the second promoter of each gene (located upstream ofarsRin the case of thehasRlocus) appears to be constitutive and weak. Quantitative transcriptional analysis in single and doublehasmutant strains revealed that σBRand σBLdirect their own transcription as well as that of their duplicates. Only a slight sensitivity in response to oxidative conditions could be assigned to either single or double mutants, revealing the probable redundancy of the σ factors implied in stress response inStreptomyces.

Roth, V., Aigle, B., Bunet, R., Wenner, T., Fourrier, C., Decaris, B., & Leblond, P. (2004). Differential and Cross-Transcriptional Control of Duplicated Genes Encoding Alternative Sigma Factors inStreptomyces ambofaciens. Journal of Bacteriology, 186(16), 5355–5365.