Figure 5.

PTF1 subunits reside on the Rbpjl proximal promoter region containing the PTF1 site in chromatin from adult pancreas. (A) ChIP analysis using antibodies to individual subunits showed that PTF1a and RBPJL, but not RBPJ, are present at or near the proximal PTF1 site. Results from a similar experiment showed PTF1a and RBPJL present at the distal PTF1 site as well (data not shown). Binding could not be detected using chromatin from adult liver. The schematic of the 1.4-Kb Rbpjl promoter shows the relative positions of the PTF1-binding sites and the primer pairs for PCR amplification. (B) Sequential ChIPs indicated that PTF1a and RBPJL coreside on Rbpjl promoters in adult acinar cells. The specificity of the consecutive enrichments was verified by the lack of enrichment with consecutive precipitations using an antibody to an unrelated DNA-binding protein (i.e., cMYC) and by the loss of any initial purification with anti-PTF1a or anti-RBPJL when anti-cMyc was used as the second precipitating antibody. Fold enrichment was quantified by quantitative PCR; a zero indicates that promoter DNA was not detected and a one indicates no enrichment relative to the input DNA.