FIG. 4.

Protection of sequences from DMS in footprinting assays correlates with requirements for mb-1 promoter activity in transfected cells. (A) Summary of results from in vivo footprinting and mb-1 promoter mutations tested in panel B. Sequences of the murine mb-1 promoter (−197 to +29, including the translational start codon) are shown with previously mapped sites of transcriptional initiation (47). Approximate binding sites for factors are labeled above and underlined between strands. Guanines and adenines protected in footprinting assays are indicated by open circles for each strand. Guanines showing enhanced cleavage (hypersensitivity) are indicated by closed circles. Mutations tested in panel B (relative to sense strand sequences) are indicated below sequences as lowercase case letters. (B) Functional requirements for mb-1 promoter factor binding sites in transfected cells. Plasmids with wild-type or mutated mb-1 promoter sequences (as in panel A) indicated at left were introduced into Ba/F3 pro-B cells, 18-81 pre-B cells, or A20 lymphoma cells in short-term transfection assays as shown. Luciferase activities were determined relative to the TATA plasmid control (see Materials and Methods) and represent the means of three experiments.