Genomic organization of the segment polarity gene pan in Drosophila melanogaster

We previously described the molecular cloning of a mammalian T cell factor (TCF-1)-like protein from Drosophila melanogaster, encoded by the pangolin (pan) locus, and demonstrated that it consists of a DNA binding domain similar to that of other high mobility group proteins and a protein-protein interaction domain that binds β-catenin (Armadillo in Drosophila) but that it lacks a transcriptional activation domain. Here we show that the pan locus spans approximately 50 kb and the mRNA results from the splicing of 13 exons. We note remarkable conservation of the exon/intron boundaries between the human and D. melanogaster genes, suggesting that they share a common ancestor. Chromosomal in situ hybridization locates pan to the base of chromosome 4, near the cubitus interruptus locus. Restriction map and sequence analyses confirm their close proximity. The small fourth chromosome undergoes little or no recombination and was previously reported to lack DNA polymorphisms; however, we note two DNA polymorphisms occurring in three combinations within the pan locus, demonstrating the presence of synonymous substitutions and the past occurrence of recombination. We present evidence suggesting that the protein encoded by pan is more similar to mammalian TCF-1 and Caenorhabditis elegans POP-1 than to mammalian LEF-1.