THE MESSENGER-RNA FOR THE 23S RIBOSOMAL-RNA METHYLASE ENCODED BY THE ERME GENE OF SACCHAROPOLYSPORA-ERYTHRAEA IS TRANSLATED IN THE ABSENCE OF A CONVENTIONAL RIBOSOME-BINDING SITE

Transcriptional analysis of the ermE gene of Saccharopolyspora erythra ea, which confers resistance to erythromycin by N-6-dimethylation of 2 3S rRNA and which is expressed from two promoters, ermEp1 and ermEp2, revealed a complex regulatory region in which transcription is initiat ed in a divergent and overlapping manner. Two promoters (eryC1p1 and e ryC1p2) were identified for the divergently transcribed erythromycin b iosynthetic gene eryC1, which plays a role in the formation of desosam ine or its attachment to the macrolide ring. Transcription from eryC1p 2 starts at the same position as that of ermEp1, but on the opposite s trand of the DNA helix, suggesting co-ordinate regulation of genes for erythromycin production and resistance. ermEp1 initiates transcriptio n at, and one nucleotide before, the ermE translational start codon. S ite-directed and deletion mutagenesis, combined with immunochemical an alysis, demonstrated that the ermEp1 transcript is translated in the a bsence of a conventional ribosome-binding site to give rise to the ful l-length 23S rRNA methylase. Deletion of the -35 region of ermEp1 redu ced, but did not abolish, promoter activity, reminiscent of the 'exten ded -10' class of bacterial promoters which, like ermEp1, possess TGN motifs immediately upstream of their -10 regions and which initiate tr anscription seven nucleotides downstream of the -10 region.