GENOMIC ORGANIZATION OF THE SEGMENT POLARITY GENE PAN IN DROSOPHILA-MELANOGASTER

We previously described the molecular cloning of a mammalian T cell fa ctor 1 (TCF-1)-like protein from Drosophila melanogaster, encoded by t he pangolin (pan) locus, and demonstrated that it consists of a DNA bi nding domain similar to that of other high mobility group proteins and a protein-protein interaction domain that binds beta-catenin (Armadil lo in Drosophila) but that it lacks a transcriptional activation domai n. Here we show that the pan locus spans approximately 50 kb and the m RNA results from the splicing of 13 exons. We note remarkable conserva tion of the exon/intron boundaries between the human and D. melanogast er 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 confi rm their close proximity. The small fourth chromosome undergoes little or no recombination and was previously reported to lack DNA polymorph isms; however, we note two DNA polymorphisms occurring in three combin ations within the pan locus, demonstrating the presence of synonymous substitutions and the past occurrence of recombination. We present evi dence suggesting that the protein encoded by pan is more similar to ma mmalian TCF-1 and Caenorhabditis elegans POP-1 than to mammalian LEF-1 .