Promoters ofMycoplasma capnicolum ribosomal RNA operons: identical activities butdifferent regulation inhomologous andheterologous cells

The 5' region of the rRNA operon, rrnA, of M. capricolumya cloned.l gequence analysis revealed two tRNA genes,tRNA and tRNA , upstreamto the promoter of the rRNA operon. The in vivo transcription start sites of the rRNAoperon and of the tRNA geneswere mapped.The same promoters used by M. capricolum RNA polymerase are also recognizedby E. coli RNA polymerase both in vivo and in vitro. We find that high levels of ppGpp in E. coli, resultingfrom aminoacid starvation or from spoT mutation, activateratherthan repressthe transcriptionof themycoplasma rrnAoperon.