FIG. 3.

Impact of PTB transient expression on levels of CAT reporter protein activity in cultured mammalian cells which were transfected with plasmids containing the poliovirus 5′NTR within the intercistronic space (Fig. 1A). CAT activities were measured 46 to 50 h following transfection and were normalized to those obtained following transfection of the null mutant pΔ87-531/SC (100%). Error bars indicate the standard deviations of results obtained in two separate experiments, each involving two replicate transfections (total of four transfections). (A) Relative CAT activities following DNA transfection of BS-C-1 cells which contain a low cytoplasmic abundance of PTB. Transfection with the null mutant, pΔ87-531/SC, generated a mean CAT activity value of 777 cpm, while CAT activity in mock-transfected cells (m) was 69 cpm. (B) Relative CAT activities in transfected H1-HeLa cells which contain a greater natural abundance of PTB than BS-C-1 cells. Transfection with the null mutant, pΔ87-531/SC, generated a mean CAT activity value of 22,715 cpm, while CAT activity in mock-transfected cells was 67 cpm.