The actin gene of the fission yeast Schizosaccharomyces pombe has been isolated by using as a hybridization probe cloned actin DNA from the budding yeast Saccharomyces cerevisiae. In contrast to most actin genes studied from diverse eukaryotic species, the S. pombe gene is not interrupted by introns. The protein sequence deduced from the nucleotide sequence of the gene shows that the S. pombe actin is more closely related to the mammalian gamma-actin than to the actin of S. cerevisiae. Three transcripts of 1240, 1650 and 1850 nucleotides having the same 5' end but differing in the length of their 3' untranslated region are generated in the fission yeast. Only one messenger RNA of 1330 nucleotides is formed from the S. pombe actin gene in S. cerevisiae. Contrary to the observation made with other S. pombe genes transcribed in the budding yeast, the heterologous actin gene transcript is initiated 39 nucleotides upstream of the initiation start site used in the homologous yeast. The mRNA termination (or 3' processing) mechanism in the two ascomycetes also differs as the 3'end of the S. pombe actin gene transcript in S. cerevisiae does not coincide with either of the three 3'ends mapped in the fission yeast.