FIG. 3.

Poly(A) signaling by different poly(A) sites. Construct pAS_w〈C₉377〉 was obtained by replacing the mutant poly(A) site of pAP_m〈C₉377〉 with an HpaI-BamHI fragment differing only at the ends from the SPA sequence used previously (18): 5′-aacaataa… tgtgtctagaactagtg-3′. Similarly, for pAL_w〈C₉377〉 the mutant poly(A) site was replaced with a SmaI-BamHI-trimmed PCR copy of the SV40 late site differing only at the ends from that used previously (18): 5′-ggggatctggac… tgggag-3′. The histogram shows the percent readthrough for the 261-nt cassette of each template relative to that of pAP_m〈C₉377〉. For the extract preparation used in these assays the citrate and Mg²⁺ concentrations were both 7 mM.