Frameshift suppression in the synthesis of Gag-Pro-Pol. Shown are the nucleotide sequences at the frameshift site and the amino acids encoded in the Gag-Pro-Pol precursors of the indicated viruses. The upper amino acid sequence is read from either the gag or pro reading frame, and the lower sequence is read from either the pro or pol reading frame, as shown. The boxes represent the indicated reading frames. The colored arrows indicate the position of the nucleotide (shown in color) that is read in both reading frames, the Vs represent the positions in the sequence that encode PR processing sites, and the numbers represent the number of nucleotides between the frameshift site and the end of the reading frame (irrespective of the nucleotide that is read in both frames). The nucleotides in the boxes include the beginning and ending codons in the reading frames shown (ASLV: avian sarcoma leucosis virus and MMTV: murine mammary tumor virus).
