GENE-EXPRESSION EVIDENCE INDICATES THAT NUCLEOTIDES-507-513 AND NUCLEOTIDES-1434-1440 IN 16S RIBOSOMAL-RNA ARE ORGANIZED IN CLOSE PROXIMITYON THE ESCHERICHIA-COLI 30S RIBOSOMAL-SUBUNIT

A non-Shine-Dalgarno translational initiator is identified in Escheric hia coli. The nucleotide sequence ACCUACUCGAGUUAG, designated as PL, i s capable of initiating translation of pokeweed antiviral protein (PAP ) and human calcitonin (hCT) mRNAs in E. coli cells. The yield of reco mbinant protein was double that obtained with the consensus Shine-Dalg arno-sequence-(SD)-driven translation. The PL sequence is composed of two heptanucleotides (ACCUACU, box I and GAGUUAC, box II) which are co mplementary to nucleotides 1434-1440 and 507-513, respectively, in 16S rRNA. Mutational analysis shows that the translation initiation effic iency with either box alone is much lower than that obtained with the entire PL sequence, indicating that the boxes interact simultaneously with both complementary regions in 16S rRNA during the translation ini tiation step. Based on these results, we propose that the two widely s eparated regions 507-513 (part of helical domain 18) and 1434-1440 (be longing to helical domain 44) are organized in close proximity to each other and to the ribosome decoding center on the surface of the E. co li 30S ribosomal subunit.