FIG. 1.

HIV-1 gene expression and frameshift signal. (A) The full-length HIV-1 mRNA encodes two precursor polyproteins, Gag and Pol, that are cleaved into their individual proteins during assembly of the mature viral particle. Abbreviations: MA, matrix; CA, capsid; NC, nucleocapsid; PR, protease; RT, reverse transcriptase; IN, integrase. (B) The HIV-1 frameshift signal is composed of two parts, the slippery sequence (UUUUUUA) and a stem-loop, a region of stable secondary structure in the mRNA. ORF, open reading frame.