Identification of a growth phase-dependent promoter in the rplJL operon of Streptomyces coelicolor A3(2)

Abstract

A single promoter, rplJp (P L10), has been identified in the rplJL operon from Streptomyces coelicolor A3(2) by promoter probe and primer extension analyses. P L10 is located upstream of the rplL gene and of the DNA encoding the mRNA leader region that contains the putative L10 (or L10.L12 4) binding site for translational autogenous regulation. The potential start point for transcription was found 239 nucleotides upstream of the predicted translational start codon of rplJ. The promoter sequence shows −35 and −10 hexamers that resemble those of Streptomyces consensus Escherichia coli σ 70-like promoters and the rplJp from Streptomyces griseus. The amount of the transcript detected by primer extension analysis decreases during growth immediately after the transition phase, a slowdown in growth occurring during exponential phase associated with increases in ppGpp level. The temporal pattern of transcripts shows a clear correlation with the temporal pattern of L10 and L7/L12 protein synthesis reported in previous kinetic studies. This indicates that P L10 is a growth phase-dependent promoter which may contribute, together with translational regulation, to the decrease in the synthesis of L10 and L7/L12 observed in liquid minimal medium. This is supported by results of promoter probe experiments. Although no significant promoter activity has been found by promoter probing in the rplJ and rplL intergenic region, an additional 5′-transcript end was detected by primer extension, probably as a result of mRNA processing event from a longer transcript. This may be required to maintain the 1:4 ratio observed for L10 and L7/L12 in the ribosomes.