FIGURE 11.

Model for the initiation of translation on SINV sgmRNAs. (A) Model of the scanning mechanism followed by SINV sgmRNA wt to initiate translation. The 40S ribosomal subunit attaches initially to the mRNA at the 5′ cap structure. Then, the 5′ UTR is scanned base-by-base in a 5′–3′ direction until the initiation codon is recognized. (B) Model for translation initiation on SINV sgmRNAs bearing two alternative start codons and a hairpin. Initially, the preinitiation complex containing the 40S ribosomal subunit interacts with the cap structure and scans the leader sequence of sgmRNA until the first AUG is encountered. Then, the 80S initiation complex can be formed and elongation ensues, leading to melting of the hairpin (hp). Another preinitiation complex starts scanning from the cap structure and skips the first AUG start codon. This preinitiation complex bearing 40S subunits can pass through the melted hairpin traveling behind the elongating 80S ribosomes. Once this 40S ribosomal subunit reaches the second AUG, synthesis of authentic C protein starts from this initiation codon.