FIG. 1.
The 16 isoforms of HIV-1 env mRNA. (A) Schematic diagram of the HIV-1 provirus genome. LTR, long terminal repeat. (B) HIV-1 provirus transcribes a genome-length 9.2-kb RNA with an m7Gppp cap and a poly(A) tail (An) containing multiple SD and SA sites. (C) Sixteen different spliced forms (isoforms) of env mRNA are present in the mRNA pool following infection with HIV-1NL4.3, and these are assembled from four alternative Env-encoding exons, designated 5E, 4bE, 4aE, and 4cE, together with 5′ noncoding exon 1 and combinations of two alternatively spliced exons, exons 2 and 3 (46). E1 to E16, cDNA plasmids pDRenv1 to pDRenv16 expressing the mRNA isoforms described in this study. (D) The env mRNAs all contain ORFs for Vpu, Env, and Nef but differ in the sequence of the 5′ UTR due to the different exons spliced together to make the mRNA.