FIG. 4.

Impact of PTB transient expression on levels of CAT reporter protein activity in cells which were transfected with plasmids (Fig. 1A) containing the HAV 5′NTR within the intercistronic space (results shown are means of four separate transfections from a total of two experiments; see the legend to Fig. 3). (A) Relative CAT activities following DNA transfection of BS-C-1 cells. Transfection with the null mutant, pΔ87-531/AC, generated a mean CAT activity value of 2531 cpm, while CAT activity in mock-transfected cells (M) was 60 cpm. (B) Relative CAT activities in transfected Huh-7 cells, which are derived from a human hepatocellular carcinoma. Transfection with the null mutant, pΔ87-531/AC, generated a mean CAT activity value of 536 cpm, while CAT activity in mock-transfected cells was 65 cpm. CAT assay incubation times were extended compared to those used in the experiments shown in Fig. 4 because of the expected low basal rate of HAV translation (78).