CHARACTERIZATION OF AN INTRONLESS COLLAGEN GENE FAMILY IN THE MARINE SPONGE MICROCIONA-PROLIFERA

Two independent clones from the genomic DNA of a marine sponge Microci ona prolifera were isolated by hybridization to the Caenorhabditis ele gans Col-1 gene and one clone was obtained from genomic DNA by PCR. Th ey contain open reading frames (MpCol1, MpCol2, MpCol3, MpCol4) capabl e of coding for a family of collagens different from those previously found in sponges. Southern blotting of genomic DNA suggested the prese nce of several other homologous genes. cDNA clones covering most of th e triple-helical coding domain and the 3' untranslated region of MpCol 1 were isolated by specific primers and reverse PCR. Two cDNA clones e nd in the middle of an AATAAA sequence 170 bp downstream from the tran slation stop codon of MpCol1. The putative NH2-terminal noncollagenous peptide is composed of only seven amino acid residues. The 1074-bp tr iple-helical coding region is not interrupted by intervening sequences . It codes for a polypeptide of 120 Gly-Xaa-Yaa triplets with only one short interruption near the COOH terminus. A putative N-glycosylation sequence (Asn-Gly-Ser), three Arg-Gly-Asp triplets known as cell reco gnition peptides, frequent Lys residues in the Yaa position (which are templates for hydroxylation), several Lys-Gly-Asn/Xaa-Arg peptides kn own as the lysyl oxidase recognition site, and long stretches without imino acids could be found within the triple-helical domain. The short COOH-terminal noncollagenous domain closely resembles that of nematod e cuticular collagens and vertebrate nonfibrillar collagens. Our resul ts strongly support the idea that the diversity of collagen genes and gene families found in higher organisms already existed in sponge.