FIG. 2.

Sequence of the chimeric virus. (A) Original sequence at the gag-pol junction in Mo-MuLV. (B) Insertion of the HIV-1 frameshift region at the Mo-MuLV gag-pol junction. The Mo-MuLV DNA sequence is given in standard uppercase letters, and the HIV-1 DNA sequence is shown in boldface. The slippery sequence of the frameshift site is enclosed in light gray. A nucleotide was changed (G→T) in the sequence between the slippery sequence and the sequence coding for the stem-loop, producing an UAG stop codon in the 0 reading frame and a codon coding for a val* in the −1 reading frame. The first base of the gag stop codon was substituted, replacing the stop codon with a glutamine codon (gln**). The cleavage sites recognized by the viral protease are indicated by arrowheads.