Expression and regulation of the rnc and pdxJ operons of Escherichia coli
Abstract
Escherichia coli rnc-era-recO operon (rnc operon) expression is negatively autoregulated at the level of message stability by ribonuclease III (RNase III), which is encoded by the rnc gene. RNase III, a double-stranded RNA-specific endoribonuclease involved in rRNA and mRNA processing and degradation, cleaves a stemloop structure in the 5' untranslated leader, initiating rapid decay of the rnc operon mRNA. Here, we examine rnc operon expression and regulation in greater detail. Northern, primer extension, and lacZ fusion analyses show that a single promoter (rncP) specifies two principal mRNAs: the 1.9 kb rnc-era transcript and the less-abundant 3.7 kb RNA encoding rnc-era-recO and the downstream pdxJ and acpS genes. A 1.3 kb pdxJ-acpS RNA is transcribed from a promoter (pdxP) located within recO. About 70% of pdxJ transcription depends on transcription from rncP. Both promoters were characterized genetically. RNase III reduces 1.9 kb and 3.7 kb transcript levels and stability, and corresponding effects are seen with genetic fusions. These detailed studies enabled us to show that the first 378 nucleotides of the rnc transcript comprise a portable RNA stability element (rncO) that contains all of the cis-acting elements required...Continue Reading
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