FIG. 7.

The TCRα: enhancer represses the TK promoter activity. (A) A schematic representation of pBLCAT2 and pBLCATαE515 plasmids. The pBLCAT2 plasmid contains the TK promoter inserted in front of the CAT transcription unit and the pBLCATαE515 carries the TCRα PvuII-PvuII 515-bp enhancer fragment cloned 5′ to the TK promoter. (B) Parental (BW5147 and L) and hybrid cells (Hy3A, Hy1B, Hy2C) were cotransfected with 15 μg of either pBLCAT2 or pBLCATαE515 together with 2 μg of pCMV-βgal DNA. CAT activities were determined and quantitated as described in the legend to Fig. 6B. The values for percent conversion, presented as means ± SDs, corresponding to pBLCAT2 and pBLCATαE515 in L, BW5147, Hy3A, Hy1B, and Hy2C are 4.08 ± 0.5, 1.22 ± 0.1, 0.91 ± 0.14, 34.3 ± 7.85, 1.75 ± 0.09, 1.06 ± 0.05, 3.16 ± 0.85, 1.7 ± 0.2, 2.61 ± 0.25, and 0.98 ± 0.13, respectively. For calculation of relative CAT activity, the activity obtained from pBLCAT2 construct in each cell line was arbitrarily assigned a value of 1. The other values observed are relative to that of pBLCAT and are the mean values of 10 independent experiments.