FIG. 3.

(A) Mutations of the SRp40 and SF2/ASF binding sites. A fragment derived from the HIV-1 env mRNA of identical length which was not predicted to contain an ESE (HIV no. 18) was used as a control fragment. Shaded boxes correspond to SF2/ASF binding sites, and nonshaded boxes correspond to SRp40 binding sites. A G-to-T mutation flanking the more 5′ predicted SF2/ASF binding site had been introduced to prevent generation of a new binding site in the cause of inactivating this site. (B) In vitro splicing assay of the dsx-GAR constructs in HeLa cells nuclear extracts.