Fig. 1.
Detection of CTCF-interacting factors by ICAT quantitative mass spectrometry. Protein samples recovered from wild-type and mutant CTCF-binding sites (Fig. S1) were labeled with the heavy and normal ICAT reagents, respectively, and prepared for μLC-MS/MS (14). SEQUEST database searching matched an MS/MS spectrum to the indicated ICAT-labeled peptide sequence derived from Scc3/SA1 as the best match. The relative abundance of isotopically heavy (Lower) and normal (Upper) ICAT-labeled peptides corresponding to Scc3/SA1 was calculated by reconstructing single-ion chromatograms for each peptide using XPRESS (14). A peptide derived from the Scc3/SA1 was enriched to a similar level (1:5.0) as peptides corresponding to CTCF (1:7.7).