Ribosome activity and modification of 16S RNA are influenced by deletion of ribosomal protein S20

A spontaneous mutant of Escherichia coli K-12 was isolated that shows an increased misreading ability of all three nonsense codons together with an inability to grow at 42° C. It is demonstrated that the mutation is a deletion of the gene rpsT, coding for ribosomal protein S20. The loss of this protein not only influences the decoding properties of the ribosome; the modification pattern of 16S ribosomal RNA is also changed. This leads to a deficiency in the ability of the mutant to associate its 30S subunits with 50S subunits to form 70S ribosomes. It is suggested that two modified bases, m⁵C and m⁶₂A, are directly or indirectly essential for association of subunits to functional ribosomes in the rpsT mutant strain. Two other modifications were also studied; m²G which is not affected at all and m³U which is undermodified in both active and inactive subunits and, therefore, not involved in subunit association.