Acetylation of ribosomal protein S5 affected by defects in the central pseudoknot in 16S ribosomal RNA?

We have analyzed the ribosomal protein profile of Escherichia coli 30S subunits with the mutation C18A in the central pseudoknot of their 16S ribosomal RNA. This mutation was shown to inhibit translational activity in vivo and to affect ribosome stability in vitro. The majority of the mutant 30S particles were present as free subunits in which a reproducible decrease in amount of proteins S1, S2, S18 and S21 was observed. The protein gels also showed the appearance of a satellite band next to S5. This band reacted with anti-S5 antibodies and had a slightly increased positive charge. The simplest interpretation of these findings, also considering published data, is that the satellite band is S5 with a non-acetylated N-terminal alanine. Underacetylation of S5 due to mutations in the 16S rRNA implies that the modification is performed on the ribosome.