Studies on ribosome structure and interactions near the m62Am62A sequence.

Antibodies raised against N6, N6-dimethyl adenosine were used to study the environment and role of the m62Am62A sequences in the E. coli ribosome. It is observed that this sequence is exposed on the surface of isolated 30S subunits, but becomes inaccessible for IgG interaction upon heat activation. The m62Am62A sequence is also inaccessible for IgG interaction in 70S ribosomes or 30S subunits immediately after dissociation of 70S particles. The presence of IgGs results in a significant inhibition of IF3 binding to unactivated 30S particles. IF3 binding to activated 30S subunits is unaffected by the IgGs. Crosslinking of 30S proteins S18 and S21 with the bifunctional phenylene dimaleimide reagents results in a reduction in the extent of 30S-IgG interaction. From what is already known about the location of S18, S21 and the IF3 binding site, it is suggested that the m62Am62A sequence is located close to the initiator tRNA binding site of the 30S subunit during initiation of protein synthesis.