The nucleotide sequence of a 3240-bp genomic fragment including the gamma -actin-encoding gene from Acremonium chrysogenum has been determined, showing an open reading frame of 1691 bp, interrupted by five introns with fungal consensus splice-site junctions. The untranslated regions of the actA gene contain a consensus TATA box, a CCAAT motif, pyrimidine stretches and the polyadenylation sequence AATAA. The predicted protein (375 amino acids) revealed high identity to gamma -actins from fungi (> 90%). Gene phylogenies constructed using DNA and protein sequences support the grouping of A. chrysogenum actin close to those from the majority of the filamentous fungi. The ActA gene is present as a single copy in the genome of A. chrysogenum; and its expression level, opposite to pcbC and cefEF cephalosporin biosynthetic genes, was steady during cephalosporin fermentation, showing a single 1.4-kb transcript.