Different processing of an mRNA species in Bacillus subtilis and Escherichia coli

Expression of the Bacillus subtilis glpD gene, which encodes glycerol-3-pho sphate (G3P) dehydrogenase, is controlled by termination or antitermination of transcription. The untranslated leader sequence of glpD contains an inv erted repeat that gives rise to a transcription terminator. In the presence of G3P, the antiterminator protein GlpP binds to glpD leader mRNA and prom otes readthrough of the terminator. Certain mutations in the inverted repea t of the glpD leader result in GlpP-independent, temperature-sensitive (TS) expression of glpD. The TS phenotype is due to temperature-dependent degra dation of the glpD mRNA. In the presence of GlpP, the glpD mRNA is stabiliz ed. glpD leader-lacZ fusions were integrated into the chromosomes of B. sub tilis and Escherichia coli. Determination of steady-state levels of fusion mRNA in B. subtilis showed that the stability of the fusion mRNA is determi ned by the glpD leader part. Comparison of steady-state levels and half-liv es of glpD leader-lacZ fusion mRNA in B. subtilis and E. coli revealed sign ificant differences. A glpD leader-lacZ fusion transcript that was unstable in B. subtilis was considerably more stable in E. coli, GlpP, which stabil izes the transcript in B. subtilis, did not affect its stability in E. coli . Primer extension analysis showed that the glpD leader-lacZ fusion transcr ipt is processed differently in B. subtilis and in E. coli. The dominating cleavage site in E. coli was barely detectable in B. subtilis. This site wa s shown to be a target of E. coli RNase III.