GENETIC AND COMPARATIVE ANALYSES REVEAL AN ALTERNATIVE SECONDARY STRUCTURE IN THE REGION OF NT-912 OF ESCHERICHIA-COLI 16S RIBOSOMAL-RNA

Mutations at position 912 of Escherichia coli 16S rRNA result in two n otable phenotypes, The C --> U transition confers resistance to strept omycin, a translational-error-inducing antibiotic, while a C --> G tra nsversion causes marked retardation of cell growth rate. Starting with the slow-growing G912 mutant, random mutagenesis was used to isolate a second site mutation that restored growth nearly to the wild-type ra te. The second site mutation was identified as a G --> C transversion at position 885 in 16S rRNA. Cells containing the G912 mutation had an increased doubling time, abnormal sucrose gradient ribosome/subunit p rofile, increased sensitivity to spectinomycin, dependence upon strept omycin for growth in the presence of spectinomycin, and slower transla tion rate, whereas cells with the G912/C885 double mutation were simil ar to wild type in these assays, Comparative analysis showed there was significant covariation between positions 912 and 885. Thus the secon d-site suppressor analysis, the functional assays, and the comparative data suggest that the interaction between nt 912 and nt 885 is conser ved and necessary for normal ribosome function, Furthermore, the compa rative data suggest that the interaction extends to include G885-G886- G887 pairing with C912-U911-C910. An alternative secondary structure e lement for the central domain of 16S rRNA is proposed.