STRUCTURE OF THE SEA-URCHIN HATCHING ENZYME GENE

The sea urchin embryo develops from an encased to a free-living larva by secreting at an early stage the hatching enzyme, a metalloprotease which hydrolyses a protective envelope derived from the egg extracellu lar matrix. Genomic clones containing the entire hatching enzyme gene were isolated from a lambda, phage sea urchin library and the complete sequence of the transcription unit was determined. The hatching enzym e gene spans 6.3 kb and comprises 9 exons. The exon/intron organizatio n of the hatching enzyme gene is similar but not identical to those of the vertebrate collagenases and stromelysins. The position and/or pha se of several introns are different even in the N-terminal moiety wher e similarity between echinoderm and vertebrate enzymes was first detec ted. The active-center domain is encoded by a 1-1 class exon whose seq uence, length and borders are highly conserved and might be considered as coding for a protein module. Adjacent to the active-center exon, t he hatching enzyme gene has an additional 1-1 exon which codes for a t hreonine-rich region. This provides further evidence that the matrix-d egrading metalloproteinases evolved by shuffling exons of the 1-1 clas s. Phylogeny analysis indicates a close relationship between the sea u rchin and vertebrate enzymes.