Figure 1.
Description of pHIV90-luc, a frameshift reporter construct. Plasmid pHIV90-luc is a derivative of pcDNA3.1/Hygro(+) (Invitrogen) in which a BamH1/XhoI fragment encoding the firefly luciferase gene sequence has been added, with an insertion at the beginning of the coding sequence corresponding to the HIV-1 gag/pol frameshift region (see Materials and Methods). The KpnI and BamHI sites were used for subcloning the HIV-1 sequence between the vector and the luciferase sequences. The AUG initiator codon is italicized. Bases from positions 8–90 (in bold) originate from HIV-1. The slippery site is UUUUUUA (underlined). It is followed by a spacer, the classic frameshift stimulatory signal (a stem–loop) and an additional 30 nt sequence. The figure presents construct (–1), which produces luciferase only when ribosomes make a –1 frameshift. Addition of an adenine at position 81 corresponds to construct (0), which produces luciferase when ribosomes do not shift the reading frame.