We report the characterization of a genomic clone containing portions of two tandemly arranged genes that encode a spicule matrix protein, SM30, of the sea urchin Strongylocentrotus purpuratus. The isolated 18.4-kilobase genomic clone contains the complete genomic sequence of one SM30 gene, designated SM30-alpha, and a portion of another SM30 gene, designated SM30-beta. Southern blot analysis shows that SM30 protein is encoded by a small gene family of two to four members. RNase protection assays indicate that the SM30-alpha gene is expressed at the time of spicule formation in the sea urchin embryo. In addition, mapping of SM30-alpha shows that a large single intron interrupts the coding sequence. Comparison of the nucleic acid and amino acid sequences of the SM30-alpha genomic sequence and the previously isolated SM30 cDNA reveals them to be very similar, but not identical. We also demonstrate that 2.6 kilobases of upstream sequence of SM30-alpha are sufficient to direct primary mesenchyme cell-specific expression of a reporter gene construct.
