A GAMETOPHYTE CELL-WALL PROTEIN OF THE RED ALGA PORPHYRA-PURPUREA (RHODOPHYTA) CONTAINS 4 APPARENT POLYSACCHARIDE-BINDING DOMAINS

A complementary DNA (cDNA) clone from a Porphyra purpurea (Roth) C. Ag ardh gametophyte-specific subtracted cDNA library was found to encode a protein containing a signal peptide and four very similar regions wi th a high degree of amino acid sequence similarity to the cellulose-bi nding domains of fungal cellulases. Northern hybridization analysis in dicated that the messenger RNA of this cDNA is highly abundant in the gametophyte but not detectable in the sporophyte. In vitro translation of the cDNA in the presence of canine pancreatic microsomes demonstra ted that the signal peptide is capable of directing the protein into t he endoplasmic reticulum where it is glycosylated. Because these obser vations suggested a possible role as a gametophyte-specific cell wall protein, cell wall proteins were isolated and a major protein having a molecular weight similar to that estimated for the encoded protein wa s purified. N-terminal sequence analysis indicated that his was the pr otein encoded by the cDNA. The abundance and organization of this prot ein suggest a role as a cell wall structural protein involved in cross linking polysaccharides.