Intersubunit RNA-protein contacts in pre- and post-translocated E. coli ribosome.

Ribosomal proteins participating in intersubunit RNA-protein contacts (directly interacting with RNA of the opposite subunit) were determined by means of ultraviolet-induced cross-links in pre- and post-translocated ribosomal complexes, as well as in the free 70 S ribosome (tight couple) of E. coli. In these 3 complexes at least L1 and L9 proteins interact with 16 S RNA, while S6, S9/11 and S15 react with 23 S RNA. All these proteins ('hinge-joint' proteins) are clustered on the small protuberance of the 50 S subunit and on the platform of the 30 S subunit. Reduction in the number of other (variable) intersubunit RNA-protein contacts in the course of transition from the tight couple to the pre- and, finally, to the post-translocated state, demonstrates gradual loosening of intersubunit interactions in 70 S ribosome. Such a loosening ('opening') of the 70 S ribosome is determined by conformational changes in ribosomal subunits and/or in their relative arrangement, conjugated with alteration of the functional state of the ribosomal complex.