A study of the thermophilic ribosomal protein S7 binding to the truncated S12–S7 intercistronic region provides more insight into the mechanism of regulation of the str operon of E. coli11This paper is dedicated to Mikhail A. Prokof’ev.

AbstractA study of the ability of His6-tagged ribosomal protein S7 of Thermus thermophilus to interact with the truncated S12–S7 intercistronic region of str mRNA of Escherichia coli has been described. A minimal S7 binding mRNA fragment is a part of the composite hairpin, with the termination codon of the S12 cistron on one side and the initiation codon of the next S7 cistron on the other. It has a length in the range of 63–103 nucleotides. The 63 nucleotide mRNA fragment, which corresponds to a putative S7 binding site, binds very poorly with S7. Tight RNA structure models, which behave as integral systems and link the S7 binding site with the translational regulation region of the hairpin, are suggested. This observation provides more insight into the mechanism of S7-directed autogenous control of translational coupling of str mRNA