Genomic organisation and polymorphism of a crustacean trypsin multi-gene family

The coding sequences of three trypsin genes, obtained by polymerase chain reaction (PCR), were determined in Penaeus vannamei (Crustacea, Decapoda). These genes were characterised by two short introns, which occur at a position quasi-conserved as the first two introns in vertebrate counterparts. Belonging to three different families, two of the genes are expressed in the digestive gland. A 5' RACE-PCR amplification of hepatopancreatic mRNA, together with the presence of short 5' extensions, confirmed that the third gene family is not expressed in this tissue. The second intron in the genes expressed in the hepatopancreas presents a 5' splice site consensus, beginning with a GC motive which is reported for the first time in trypsin genes and is of phase I in mammals. A high copy number was determined for these genes. Several restricted PCR were performed to describe the polymorphism of these sequences. Five genes were partially sequenced for each family and five genes coding the different, previously described cDNAs were recovered. These sequences also confirm that the third family resembles a mosaic of type I and type II gene families. A high degree of polymorphism in the introns (54-59% identity) among the three families is observed, but mutations in corresponding introns inside each of the families are low (3-6%).