Interaction between the ribosomal subunits: 16S rRNA suppressors of the lethal DeltaA1916 mutation in the 23S rRNA of Escherichia coli.

A1916 in 23S rRNA is located in one of the major intersubunit bridges of the 70S ribosome. Deletion of A1916 disrupts the intersubunit bridge B2a, promotes misreading of the genetic code and is lethal. In a genetic selection for suppressor mutations, two base substitutions in 16S rRNA were recovered that restored viability and also allowed expression of DeltaA1916-associated capreomycin resistance. These mutations were G1048A in helix 34 and U1471C in helix 44. Restoration of function is incomplete, however, and the double mutants are slow-growing, defective in subunit association and support high levels of translational errors. In contrast, none of these parameters is affected by the single 16S suppressor mutations. U1471C likely affects another intersubunit contact, bridge B6, suggesting that interactions between different bridges and cross-talk between subunits contributes to ribosomal function.