Isolation and cloning of Ser4, a gene encoding a trypsin-like serine protease in Drosophila melanogaster

A gene encoding a unique serine protease in Drosophila melanogaster was characterized using overlapping cDNA and genomic clones. The sequence contains an open reading frame of 798 base pairs encoding a predicted protein 265 amino acids in length with significant homology to other serine proteases. The deduced amino acid sequence of this protein contains several structural features which are highly conserved in active serine proteases, including conserved cysteine and active site residues. Northern blot analysis reveals that the mRNA for the gene is expressed abundantly in the larval gut, suggesting a role in digestion for this protein. Using in situ hybridization to polytene chromosomes, we have localized this gene to region 56E3 on chromosome 2R.