Fig. 1. Schematic representation of the splicing patterns of wild-type and U-to-C mutant HIV-1pm213 pre-mRNAs. The structure of the HIV-1 genome is indicated, along with the location of the Rev response element (RRE). Coding exons are represented by open boxes. The main splice products for the wild-type (HIV-1pm213) and mutant (HIV-1pm213, L1 derivate) pre-mRNAs are indicated, together with the 5′ and 3′ splice sites and their positions in the viral transcript. The relative percentage of total HIV-1 messages representing the unspliced gag–pol messages are indicated for both viral clones (Wentz et al., 1997). Shaded boxes represent untranslated regions present in the final messages. Figure based on Wentz et al. (1997).