FIG. 4.

Basal promoter function of the wild-type BLV U3 and 25 LTR mutants in the absence (A) and presence (B) of p34Tax (solid bars) with values in the absence of p34Tax (open bars) shown for comparison. LTRs were inserted into a CAT reporter construct and transfected into BLV-negative Tb₁Lu cells with or without cotransfection with a tax-containing plasmid. Mutants are arranged according to their location on the U3 map (Fig. 1). Promoter activity was measured as nanograms of CAT protein per 10 μg of total protein, and values were standardized by scaling the activity of the wild-type LTR to 1.0. Each value is the mean of five (A) or two (B) trials in separate experiments. Asterisks indicate that the CAT activity of the mutant is significantly different from the wild-type LTR (P ≤ 0.05 [Dunnett t test]). Abbreviations: a, addition; d, deletion; s, substitution; WT, wild type. Acronyms in capital letters refer to sites illustrated in Fig. 1.