Hicks K A, Grossman A D
Department of Biology, Massachusetts Institute of Technology, Cambridge 02139, USA.
J Bacteriol. 1995 Jul;177(13):3736-42. doi: 10.1128/jb.177.13.3736-3742.1995.
spo0H encodes a sigma factor, sigma-H, of RNA polymerase that is required for sporulation in Bacillus subtilis. Null mutations in spo0H block the initiation of sporulation but have no obvious effect on vegetative growth. We have characterized an insertion mutation, csh203::Tn917lac, that makes spo0H essential for normal growth. In otherwise wild-type cells, the csh203::Tn917lac insertion mutation has no obvious effect on cell growth, viability, or sporulation. However, in combination with a mutation in spo0H, the csh203 mutation causes a defect in vegetative growth. The csh203::Tn917lac insertion mutation was found to be located within orf23, the first gene of the rpoD (sigma-A) operon. The transposon insertion separates the major vegetative promoters P1 and P2 from the coding regions of two essential genes, dnaG (encoding DNA primase) and rpoD (encoding the major sigma factor, sigma-A) and leaves these genes under the control of minor promoters, including P4, a promoter controlled by sigma-H. The chs203 insertion mutation caused a 2- to 10-fold increase in expression of promoters recognized by RNA polymerase containing sigma-H. The increased expression of genes controlled by sigma-H in the csh203 single mutant, as well as the growth defect of the csh203 spo0H double mutant, was due to effects on rpoD and not to a defect in orf23 or dnaG.
spo0H编码一种RNA聚合酶的σ因子，即σ-H，它是枯草芽孢杆菌芽孢形成所必需的。spo0H中的无效突变会阻断芽孢形成的起始，但对营养生长没有明显影响。我们鉴定了一个插入突变体csh203::Tn917lac，它使spo0H成为正常生长所必需的。在其他方面为野生型的细胞中，csh203::Tn917lac插入突变对细胞生长、活力或芽孢形成没有明显影响。然而，与spo0H中的突变相结合时，csh203突变会导致营养生长缺陷。发现csh203::Tn917lac插入突变位于rpoD（σ-A）操纵子的第一个基因orf23内。转座子插入将主要的营养启动子P1和P2与两个必需基因dnaG（编码DNA引物酶）和rpoD（编码主要的σ因子，σ-A）的编码区域分开，并使这些基因处于次要启动子的控制之下，包括由σ-H控制的启动子P4。chs203插入突变导致由含有σ-H的RNA聚合酶识别的启动子的表达增加2至10倍。csh203单突变体中由σ-H控制的基因表达增加，以及csh203 spo0H双突变体的生长缺陷，是由于对rpoD的影响，而不是由于orf23或dnaG的缺陷。
