Actin represents one of the most highly conserved families of proteins in evolution. The work presented here describes the molecular characterization of the mouse smooth muscle (enteric) gamma-actin gene (SMGA). It represents the largest isoactin gene characterized to date, measuring over 23,000 bp from the transcription start site to the polyadenylation signal. The gene is divided into nine exons and encodes a mature actin protein of 374 amino acids. Putative regulatory elements are noted as well as regions of the gene that have the potential to form non-B DNA conformations that may influence gene expression.