AN EXTREMELY HIGH CONSERVATION OF RNA-PROTEIN S7 INTERACTIONS DURING PROKARYOTIC RIBOSOMAL BIOGENESIS

Direct determination of RNA-protein complex structures is often facili tated by the use of thermophilic proteins; however E.coli is the most investigated system so far. A hybrid approach is to form heterologous complexes of E.coli RNA with thermophilic proteins. The rationale for this approach to RNA-protein interactions in ribosomes is based on the ability of the thermophilic protein S7 to replace a homologous counte rpart in vivo. In vitro, the protein S7 of Thermus thermophilus is abl e to form complexes with both the minimal 16S rRNA fragment and the in tercistronic region of the str operon mRNA from E.coli (K-d = 1.4 x 10 (-7) M and 1.1 x 10(-7) M respectively). The interaction of Thermus S7 with the E. coli intercistronic mRNA is surprising, because this regi on does not exist in the thermophilic str operon. It suggests a high d egree of conservation of an RNA binding site on S7.