Figure 4.

Overexpression of SMRT potentiates the LAZ3/BCL6-mediated repression. The LAZ3/BCL6 encoding vector (pTL1-LAZ3/BCL6) was transfected without (−) or with (+) the SMRT encoding vector (pCMX-SMRT) (hatched bars). The coexpression of LAZ3/BCL6 and SMRT elicits a ≈ 2-fold increase in the LAZ3/BCL6-mediated repression of the B6BS reporter activity (18). Cotransfection of pCMX-SMRT with the empty pTL1 vector results in a slight decrease of the B6BS reporter activity, as compared with the mock transfected cells (empty bars). This is presumably due to the weak expression of the endogenous LAZ3/BCL6 protein in C2 cells (ref. 15, data not shown). Either empty pTL or pTL-LAZ3/BCL6 (17) expression vector was transfected together with B6BS-tkLuc (1.5 μg) (18), and with either empty pCMX or pCMX-SMRT expression vector (0.2 μg). pSG5-β-gal (0.1 μg) was cotransfected in each assay to correct for variation in transfection efficiency. Results are expressed as normalized luciferase activity.