(A) A schematic representation of construct Td3 and its different modifications. Boxed TTT in construct T3Td3 denote a substitution of three consecutive G residues in construct Td3 for three T residues. Other designations are as in Fig. 1A. (B) Toeprint analysis of 48S initiation complexes assembled on mRNAs bG, Td3, Td5, Td6, bTd3, and Td3b. A dideoxynucleotide sequence generated with the same primer corresponds to construct Td3. (C) Toeprint analysis of 48S initiation complexes reconstituted with model mRNAs bTd5 and T3Td3. For comparison, the complexes assembled on Td3 and bG were analyzed in parallel. A dideoxynucleotide sequence generated with the same primer corresponds to construct Td3.