Ribosomal protein S1 and initiation factor IF3 do not promote the ribosomal binding of ~ 19-nucleotide-long mDNA and mRNA models

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Abstract
A number of model mDNAs and mRNAs, about 19 nucleotides in length, were obtained by automated synthesis and T7 RNA polymerase directed transcription from synthetic DNA templates, respectively. These mDNAs and mRNAs had Shine-Dalgarno sequences that were four to eight nucleotides long and their sequence was similar to the R17 coat protein initiation site. The effect of S1 or initiation factors (IFs) on the rate and extent of ribosomal binding of these mDNAs and mRNAs was investigated by nitrocellulose filtration. No effect was detected, suggesting that the main function of S1 or IFs included neither the direct recognition or binding of short messengers to the 30S subunits, nor their rejection as "false" for possessing the wrong sugars or an insufficient length. A pulse–chase experiment with one of the mRNAs also showed that S1 or IF3 did not influence the exchange rate of mRNA bound to the 30S subunit.Key words: ribosome, initiation, mRNA, ribosomal protein S1, initiation factor IF3.