Postexponential regulation of sin operon expression in Bacillus subtilis

  • Shafikhani S
  • Mandic-Mulec I
  • Strauch M
 et al. 
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Abstract

The expression of many gene products required during the early stages of Bacillus subtilis sporulation is regulated by sinIR operon proteins. Transcription of sinIR from the P1 promoter is induced at the end of exponential growth. In vivo transcription studies suggest that P1 induction is repressed by the transition-state regulatory protein Hpr and is induced by the phosphorylated form of Spo0A. In vitro DNase I footprinting studies confirmed that Hpr, AbrB, and Spo0A are trans-acting transcriptional factors that bind to the P1 promoter region of sinIR. We have also determined that the P1 promoter is transcribed in vitro by the major vegetative sigma factor, ␴ A , form of RNA polymerase. Natural environments are oligotrophic (35). Organisms such as the common soil bacterium Bacillus subtilis frequently exist in slow-or nongrowing physiological states. The rich diversity of B. subtilis transition-state regulatory systems (50, 55, 56) confirms the biological importance of managing the transition from rapid-to slow-to nongrowing cell states. Depending on the environmental cues present, B. subtilis transition-state reg-ulation can channel a cell toward motility, nutrient scavenging through the production of extracellular enzymes, competence, or sporulation cell fates (for a review, see references 12 and 53). The best-characterized B. subtilis transition-state regula-tors are the AbrB, Hpr, Spo0A, and SinR DNA-binding pro-teins. Recent structural studies have shown that the AbrB protein is a tetramer of 10,500-Da subunits that interacts with a variety of specific nucleotide sequences, presumably by recognizing a particular three-dimensional DNA architecture (54, 59, 62). AbrB can function as a repressor of genes such as spo0E, spo0H, spoVG, and aprE (14, 34, 43, 64) and as an activator of genes such as hpr and the rbs operon (52, 53). Transcription of abrB is controlled by negative autoregulation and repression by Spo0A (53, 55). The hpr gene product is a 23,718-Da protein, which was originally identified as a locus (hpr, scoC, and catA) for mutations causing protease overproduction and catabolite-resistant sporulation (10, 21, 39). Hpr binds to a consensus DNA sequence RATAnTATY (25, 53). Hpr represses the expression of the protease genes aprE and nprE and oligopep-tide permease operons (20, 26) and when present on a multi-copy plasmid can inhibit sporulation in an as-yet-undetermined manner (39). The Spo0A 29,691-Da protein is the master con-troller of early developmental events (55, 56). Metabolic and environmental signals cause the autophosphorylation of sensor

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