Cloning and sequence of a gene encoding the L7/L12 ribosomal protein equivalent of Streptomyces antibioticus

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

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 sigma(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.

Synthesis of ribosomal proteins during growth of Streptomyces coelicolor

Changes in expression of ribosomal protein genes during growth and stationary phase of Streptomyces coelicolor A3(2) in liquid medium were studied. Proteins being synthesized were pulse-labelled with [35S]-methionine, separated by two-dimensional polyacrylamide gel electrophoresis, and quantified using the BioImage computer software. Most of the ribosomal proteins were synthesized throughout the life cycle. Exceptions were two proteins whose synthesis drastically decreased at the approach of stationary phase. These two proteins were identified in purified ribosomes as homologues of Escherichia coli ribosomal proteins L10 and L7/L12, using antibodies raised against fusion proteins between these ribosomal proteins and Escherichia coli beta-galactosidase. The genes (rplJ and rplL) encoding the L10 and L7/L12 proteins were contained in a 1.2 kb BamHI fragment that was cloned and sequenced. The linkage and order of the genes coincide with other L10-L7/L12 operons. However, L11 and L1 genes were not present immediately upstream of the L10 gene, as is the case for E. coli and other bacteria. Instead, two open reading frames of unknown function were found immediately upstream of the L10 gene, in an adjacent 1.9 kb BamHI fragment.