The human CCG1 gene, encoding CCG1/TAFII250/p250, was isolated by complementing tsBN462, a mutant BHK21 cell line that shows cell-cycle arrest at high temperature. Using the cDNA as a probe, the locations of exon-intron junctions were determined in the genomic DNA. Thirty-eight exons ranging from 68 to 219 bp in size were found. All the exon-intron junctions followed the GT-AG rule. Using a newly developed method, we performed a module analysis of the CCG1 protein. The functional domain previously predicted in CCG1 was further confirmed to be encoded in a single predicted module that is the minimal functional unit in the protein. The boundaries of the predicted modules show a close correlation to the intron/exon junction of CCG1. The entire gene, at least 110 kb long, has been recovered in a YAC, which provides a route to the further study of module function.