Title

Autoinduction of Bacillus subtilis phoPR Operon Transcription Results from Enhanced Transcription from E^A- and E^E-Responsive Promoters by Phosphorylated PhoP.
Salbi Paul, 2004.The phoPR operon encodes a response regulator, PhoP, and a histidine kinase, PhoR, which activate or repress genes of the Bacillus subtilis Pho regulon in response to an extracellular phosphate deficiency . Induction of phoPR upon phosphate starvation required activity of both PhoP and PhoR, suggesting autoregulation of the operon, a suggestion that is supported here by PhoP footprinting on the phoPR promoter . Primer extension analyses, using RNA from JH642 or isogenic sigE or sigB mutants isolated at different stages of growth and/or under different growth conditions, suggested that expression of the phoPR operon represents the sum of five promoters, each responding to a specific growth phase and environmental controls . The temporal expression of the phoPR promoters was investigated using in vitro transcription assays with RNA polymerase holoenzyme isolated at different stages of Pho induction, from JH642 or isogenic sigE or sigB mutants . In vitro transcription studies using reconstituted E

^A, E

^B, and E

^E holoenzymes identified P_A4 and P_A3 as E

^A promoters and P_E2 as an E

^E promoter . Phosphorylated PhoP (PhoP

P) enhanced transcription from each of these promoters . E

^B was sufficient for in vitro transcription of the P_B1 promoter . P₅ was active only in a sigB mutant strain . These studies are the first to report a role for PhoP

P in activation of promoters that also have activity in the absence of Pho regulon induction and an activation role for PhoP

P at an E

^E promoter . Information concerning P_B1 and P₅ creates a basis for further exploration of the regulatory coordination or overlap of the PhoPR and SigB regulons during phosphate starvation .

The dinB Operon and Spontaneous Mutation in Escherichia coli.
Gregory J. McKenzie, 2003.Apparently conflicting data regarding the role of SOS-inducible, error-prone DNA polymerase IV (DinB) in spontaneous mutation are resolved by the finding that mutation is reduced by a polar allele with which dinB and neighboring yafN are deleted but not by two nonpolar dinB alleles . We demonstrate the existence of a dinB operon that contains four genes, dinB-yafN-yafO-yafP . The results imply a role for yafN, yafO, and/or yafP in spontaneous mutation .

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