FIG. 3.

An Sp1 site confers butyrate responsiveness to the ORF50 promoter. (A) Schematic diagram of sequence replacement mutants in the ORF50 promoter. Numbers indicate the corresponding positions of nucleotides in the ORF50 promoter map upstream of the translation start site. The putative Sp1 site is located at 103 to 112; the putative TATA box is from 61 to 68. The sequence in boldface type represents linker DNA used to replace various regions in the ORF50 promoter to generate mutant constructs (m1 to m5). The putative Sp1 site is in italics; the putative TATA element is underlined. Wt, wild type; m, mutant. (B) Luciferase assay of ORF50 promoter mutants. HH-B2 cells were transfected and treated with drugs as described in the legend to Fig. 2. C, control (unreated); B, butyrate; T, TSA. The numbers below the bars indicate the induction (n-fold) of reporter activity in butyrate-treated cells compared to untreated HH-B2 cells.