Spira B, Yagil E
Department of Biochemistry, George S. Wise Center for Life Sciences, Tel-Aviv University, Israel.
Mol Gen Genet. 1998 Feb;257(4):469-77. doi: 10.1007/s004380050671.
Starving of Escherichia coli cells for inorganic orthophosphate (Pi) results in the accumulation of spoT-dependent ppGpp and induces the expression of genes of the PHO regulon. In a delta relA delta spoT strain that is unable to accumulate ppGpp the expression of two genes (phoA and pstS) that belong to the PHO regulon is impaired, even in constitutive mutants. The transcription of phoA and of pstS is not affected in the ppGpp0 strain, and therefore this impairment is due to a post-transcriptional defect. Conversely, overexpression of ppGpp inhibits transcription of these two PHO regulon genes. In phoB mutants, the accumulation of ppGpp during Pi starvation is diminished, suggesting that PhoB or one of the PHO products is involved in the control of ppGpp accumulation. We propose that the presence of ppGpp in the cell, but not its accumulation as a result of the starvation stress, is important for the expression of the PHO genes.
使大肠杆菌细胞缺乏无机正磷酸盐（Pi）会导致spoT依赖性ppGpp的积累，并诱导PHO调节子基因的表达。在无法积累ppGpp的ΔrelAΔspoT菌株中，即使在组成型突变体中，属于PHO调节子的两个基因（phoA和pstS）的表达也会受损。phoA和pstS的转录在ppGpp0菌株中不受影响，因此这种损伤是由于转录后缺陷所致。相反，ppGpp的过表达会抑制这两个PHO调节子基因的转录。在phoB突变体中，Pi饥饿期间ppGpp的积累减少，这表明PhoB或一种PHO产物参与了对ppGpp积累的控制。我们提出，细胞中ppGpp的存在，而非由于饥饿应激导致的其积累，对PHO基因的表达很重要。
