Involvement of bases 787-795 of Escherichia coli 16S ribosomal RNA in ribosomal subunit association

A nine-base DNA oligomer [d(GTATCTAAT)] was used to probe the accessibility and function of bases in the region 787-795 of Escherichia coli 16S rRNA. Hybridization of the cDNA [d(GTATCTAAT)] to 16S rRNA in situ was carried out by binding the probe to intact 30S ribosomal subunits. Nitrocellular filter binding showed that cDNA hybridization saturated with increasing probe concentration, suggesting that the probe was binding to a discrete site or sites. RNase H digestion of the rRNA under the DNA·rRNA hybrid and sequencing of the resultant RNA fragments verified that the cDNA probe bound specifically to the 787-795 region. Hybridization experiments using the cDNA probe showed that bases in the 787-795 region of 165S rRNA are exposed on the surface of 30S subunits. The functional role of bases 787-795 was then tested by assaying various ribosomal activities with the cDNA in place. Results of these functional assays demonstrate that this 16S rRNA region is directly involved in the association of 30S and 50S subunits.