Figure 1.

Schematic diagram of the vectors used to measure programmed −1 ribosomal frameshift efficiencies in vivo. Transcription is driven from the PGK1 promoter and uses the PGK1 translation initiation codon. In pTI25, the bacterial lacZ gene is in the 0-frame with respect to the start site. In plasmid pF8, the lacZ gene is positioned 3′ of the L-A virus frameshift signal and in the −1 frame relative to the translation start site.