Abstract
Southern transfer and solution hydridization experiments, using as probe a DNA fragment that encodes Drosophila actin, demonstrate cross hybridization to DNA from the sea urchin S. purpuratus. Recombinant DNA clones that contained sea urchin genomic DNA fragments were constructed and screened for the presence of actin-encoding DNA sequences by colony hybridization with the Drosophila actin sequence. Two different putative actin-encoding clones specifically hybridized actin-encoding mRNA from a complex mRNA population. Southern blot hybridization experiments with both the Drosophila actin sequence and 1 of the cloned sea urchin sequences, in conjunction with solution hybridization data, suggest an actin gene copy number of 5-20 per haploid genome. DNA sequence analysis of 1 of the cloned sequences indicates that this fragment codes for a cytoplasmic form of actin and contains an intervening sequence of at least 200 nucleotides beginning immediately after amino acid 121 in the protein sequence.