Cell wall biogenesis in Chlamydomonas: molecular characterization of a novel protein whose expression is up-regulated during matrix formation

Abstract

In the unicellular eukaryote Chlamydomonas, disruption of cell-matrix interactions by treatment with a periplasmic matrix metalloproteinase, g-lysin, activates a signal transduction pathway that results in the rapid synthesis and secretion of matrix molecules, followed by their assembly into a new matrix. I have identified and partially characterized several cDNA clones for transcripts that are dramatically up-regulated following treatment of cells with g-lysin. Here I report the complete nucleotide sequence and preliminary characterization of a matrix-related molecule termed Mrp47. The cDNA clone for Mrp47 contained an insert of 2.5 kb, corresponding to a transcript of 3.0 kb that is encoded by a single-copy gene. Sequence analysis indicated that Mrp47 cDNA contains an open reading frame (ORF) that encodes a 46-kDa polypeptide. The putative polypeptide is unusually rich in the amino acids proline, alanine and serine, with prolines clustered together in a 30-amino acid N-terminal region and a 80-amino acid C-terminal region. Further analysis of the predicted amino acid sequence suggested that Mrp47 is likely to be a secreted glycoprotein. Southern hybridization analysis indicated that Mrp47 is encoded by a single-copy gene in the Chlamydomonas genome. Database searches suggested that Mrp47 shows homology to other proline-rich proteins including a surface glycoprotein in Volvox and verprolin from yeast.