MUTATIONAL ANALYSIS OF 2 HIGHLY CONSERVED UGG SEQUENCES OF 23 S RIBOSOMAL-RNA FROM ESCHERICHIA-COLI

The 23 S-type rRNA contains two phylogenetically conserved UGG sequenc es, which have the potential to bind the universal CCA-3'-ends of tRNA s at the ribosomal peptidyltransferase center by base pairing. The fir st two positions, UG, of these sequences at the helix-loop 80 (U2249G2 250) and helix-loop 90 (Psi 2580G2581) and some related nucleotides we re tested by site-directed mutagenesis for their involvement in riboso mal function, i.e. peptidyltransferase. The plasmid derived mutated 23 S rRNA comprised about 50% of the total 23 S rRNA, None of the single mutations caused an assembly defect, and all 50 S subunits carrying a n altered 23 S rRNA could freely exchange with the pools of 70S riboso mes and polysomes, The mutations at the helix-loop 80 region hardly af fected bacterial growth. However, mutations at the helix 90 caused sev ere growth effects and severely impaired the in vitro protein synthesi s, showing that this 23 S rRNA region is of high importance for riboso mal function.