Formylmethionyl-tRNA Binding Properties of <em>Escherichia coli</em> Ribosomal Protein S1.

Formylmethionyl-tRNA has been found to bind to Escherichia coli ribosomal protein SI. Com- plexes of S1 and methionine-labeled fMet-tRNA_f^Met were detected by binding to cellulose nitrate membranes. Complex formation was stimulated by incubation at low ionic strength, at 37°C and in the absence of Mg²⁺. Protein S1 also bound [³H]poly(rC) under the same conditions or in buffers of higher ionic strength, 10 mM in Mg²⁺, and during incubation at 0°C. Unlabeled poly(rC) was an effective inhibitor of the binding of labeled fMet-tRNA when both nucleotides were added simultaneously to the reaction mixtures; however, approximately 80% of previously bound f[³⁵S]Met-tRNA remained bound after the subsequent addition of unlabeled poly(rC). Binding of f[3sS]Met- tRNA, but not the binding of [³H]poly(rC), was inhibited by polyamines or aminoglycoside antibiotics. Protein S1 that had been reacted with N-ethylmaleimide failed to bind f[3sS]Met-tRNA but was still capable of binding [³H]poly(rC). The data support the concept of two distinct RNA-binding sites on the S1 molecule. Initiator tRNA appears to occupy a site concerned with the RNA unwinding property of S1, whereas poly(rC) binds primarily at a separate site. During initiation on the ribosome, the poly(rC) site may interact with the 3′ end of 16-S ribosomal RNA, while the other site may interact with either mRNA or fMet-tRNA. [ABSTRACT FROM AUTHOR]