An 1830-bp genomic DNA segment containing an Arabidopsis thaliana actin gene, AAc1, has been cloned and sequenced. The AAc1 gene is present as a single-copy gene, but at least two other actin-like genes have been detected. Comparison of the nucleotide sequence of AAc1 with other cloned plant actin genes reveals four exons separated by three introns conservatively located in all plant actin genes. The deduced amino acid sequence has also been compared with actin protein sequences from other plants.