Mapping contacts of the S12–S7 intercistronic region of str operon mRNA with ribosomal protein S7 of E. coli

In E. coli, S7 initiates 30S ribosome assembly by binding to 16S rRNA. It also regulates translation of the S12 and S7 cistrons of the ‘streptomycin’ operon transcript by binding to the S12–S7 intercistronic region. Here, we describe the contacts of N-terminally His6-tagged S7 with this region as mapped by UV-induced cross-linking. The cross-links are located at U(−34), U(−35), quite distant from the start codons of the two cistrons. In order to explain the mechanism of translational repression of S12–S7, we consider a possible conformational rearrangement of the intercistronic RNA structure induced by S7 binding.