The ACC1 gene, encoding acetyl-CoA carboxylase, is essential for growth in Ustilago maydis.

Acetyl-CoA carboxylase [ACCase; acetyl-CoA:carbon dioxide ligase (ADP forming), EC 6.4.1.2] catalyses the ATP-dependent carboxylation of acetyl-CoA to form malonyl-CoA. We have amplified a fragment of the biotin carboxylase (BC) domain of the Ustilago maydis acetyl-CoA carboxylase (ACC1) gene from genomic DNA and used this amplified DNA fragment as a probe to recover the complete gene from a lambda EMBL3 genomic library. The ACC1 gene has a reading frame of 6555 nucleotides, which is interrupted by a single intron of 80 bp in length. The gene encodes a protein containing 2185 amino acids, with a calculated M(r) of 242,530; this is in good agreement with the size of ACCases from other sources. Further identification was based on the position of putative binding sites for acetyl-CoA, ATP, biotin and carboxybiotin found in other ACCases. A single ACC1 allele was disrupted in a diploid wild-type strain. After sporulation of diploid disruptants, no haploid progeny containing a disrupted acc1 allele were recovered, even though an exogenous source of fatty acids was provided. The data indicate that, in U. maydis, ACCase is required for essential cellular processes other than de novo fatty acid biosynthesis.