Internal initiation of wild-type ribosomes. The constructs analyzed are shown on the left, with the type of ribosomes present in the cells. The ratio of luciferase activity to β-galactosidase activity measured for each construct is shown in the right box plot, as arbitrary units. Translations of the lacZ gene by wild-type ribosomes (WT), and of the luc gene with either a wild-type SD (wt SD) (dark gray) or no SD (black) by wild-type ribosomes (A). Translations of lacZ by wild-type ribosomes, and of luc with either no SD (black) or a oSD (light gray) by wild-type ribosomes (1), or a oSD (hatched) by wild-type and oRibo-T ribosomes (2) (B). Translations of lacZ by oRibo-T ribosomes and of luc with either no SD (black) or a oSD (light gray) by wild-type and oRibo-T ribosomes (C), or by oRibo-T ribosomes with (light gray) or without (black) a stem-loop structure upstream from luc (D). The SmaI site specific of the sequence without a stem−loop structure is indicated. Results are from at least six independent experiments.