Genes for two subunits of acetyl-coenzyme A carboxylase, biotin carboxylase and biotin carboxyl carrier protein, have been cloned from Anabaena sp. strain PCC 7120. The two proteins are 181 and 447 amino acids long and show 40 and 57% identity to the corresponding Escherichia coli proteins, respectively. The sequence of the biotinylation site in Anabaena sp. strain PCC 7120 is MetLysLeu, not the MetLysMet found in other sequences of biotin-dependent carboxylases. The amino acid sequence of biotin carboxylase is also very similar (32 to 47% identity) to the sequence of the biotin carboxylase domain of other biotin-dependent carboxylases. Genes for these two subunits of acetyl-coenzyme A carboxylase are not linked in Anabaena sp. strain PCC 7120, contrary to the situation in E. coli, in which they are in one operon.