BACILLUS-POPILLIAE CRY18AA OPERON IS TRANSCRIBED BY SIGMA(E) AND SIGMA(K) FORMS OF RNA-POLYMERASE FROM A SINGLE INITIATION SITE

Bacillus popilliae is an obligate pathogen for larvae of the insect fa mily Scarabaeidae (Coleoptera). It forms parasporal crystals upon spor ulation. The gene cry18Aa coding for the parasporal crystal protein an d an upstream open reading frame, orf1, were previously isolated from B.popilliae, Here we report an analysis of cry18Aa transcription in Ba cillus thuringiensis, The only transcriptional start site of cry18Aa w as found 29 bp upstream of the open reading frame orf1, suggesting tha t orf1 and cry18Aa are transcribed as an operon, lacZ fusion to the cr y18Aa promoter was used to follow the time-course of cry18Aa transcrip tion in wild type B.thuringiensis and in various B.thuringiensis sporu lation-deficient mutants (spo0A, sigE or sigK), In wild type B.thuring iensis, the cry18Aa promoter was activated 2 h after the end of expone ntial growth and the expression lasted to the late sporulation phase, The results of promoter activity in Spo(+) or Spo(-) backgrounds toget her with the results of primer extension experiments suggest that the transcription from this promoter can be driven by both sigma(E) and si gma(K) types of RNA polymerase at a single start site, The promoter re gion of cry18Aa operon fits the consensus sequences of both sigma(E) a nd sigma(K) dependent promoters of Bacillus.