Translation of Tat1 and Tat2 RNAs in the untreated RRL system. The top three lanes depict the Glob-Fluc, UTRTat1-Rluc and UTRTat2-Rluc RNAs used in the translation assays in the untreated RRL (URRL). The vertical bar in the 5'UTR of Tat2 represents exon EX' (See fig. 1). Tat1 and Tat2 RNAs were translated in the URRL in the presence of a large excess of endogenous globin mRNA and of in vitro generated Glob-Fluc RNA. Independent experiments showed that 50 ng of Glob-Fluc RNA were saturating the URRL. Therefore 50 ng of Glob-Fluc RNA (grey bars) were used per assay together with increasing amounts of UTRTat1-Rluc (white bars) or UTRTat2-Rluc RNA (black bars). Note that under these stringent competition conditions, namely an excess of endogenous globin mRNA as well as Glob-Fluc RNA, UTRTat1/2 RNA at 5 ng (1 × 10-9 M) were well translated (white and black bars, respectively).