Calcium-pumping ATPases are an essential component of the intracellular calcium homeostasis system and have been characterized in a large variety of species and cell types. In mammalian genomes, these proteins are encoded by gene families whose individual members feature complex tissue-specific expression and alternative splicing. In the search for a less complex system that is more amenable to genetic manipulation, we have identified a family of three genes (mca-1, mca-2, and mca-3) encoding putative calcium ATPases in the Caenorhabditis elegans Genome Project data and completed their transcript structure. In this work, we report the cloning and functional expression of the mca-1 gene, which encodes a calcium-stimulated ATPase whose features resemble those of the plasma membrane calcium adenosine triphosphatase family of mammalian cells and appears to be regulated by a multipartite promoter.