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Yeast Mutants Defective in Acetyl‐Coenzyme A Carboxylase and Biotin: Apocarboxylase Ligase

1980; Wiley; Volume: 111; Issue: 1 Linguagem: Inglês

10.1111/j.1432-1033.1980.tb06077.x

1432-1033

Masayoshi Mishina, Rainer ROGGUENKAMP, Eckhart Schweizer,

Electrochemical sensors and biosensors

Among more than 7000 mutants of Saccharomyces cerevisiae , requiring saturated fatty acids, 61 acetyl‐CoA‐carboxylase‐deficient strains have been identified. According to their mutual complementation characteristics these mutants have been assigned to two different genes, acc1 and acc2 . Both acetyl‐CoA carboxylase genes tire unlinked to each other and to the fatty acid synthetase genes fas1 and fas2 . The acetyl‐CoA carboxylases of several acc1 and acc2 mutants have been purified and assayed for their overall and component enzyme activities. Besides overall acetyl‐CoA carboxylation, which was lost in all cases, both component enzymes, biotin carboxylase and transcarboxylase, were simultaneously affected in most mutants, though often to a different relative extent. Similarly, the comparison of biochemical and genetic complementation data revealed no basis for a clear distinction between specific biotin carboxylase and transcarboxylase mutants. These results Suggest that accl is a cluster gene coding for a multifunctional protein harboring both acetyl‐CoA carboxylase component enzyme activities on the same polypeptide chain. The acetyl‐CoA carboxylase isolated from acc2 mutants was free of biotin. Correspondingly, biotin:apoacetyl‐CoA‐carboxylase ligase activity was missing in acc2 mutants. Therefore, it is concluded that the primary defect in acc2 mutants is in the biotin:apocarboxylase ligase. In agreement with this conclusion, the acc2 acetyl‐CoA carboxylase can be activated, in the presence of biotin and ATP, by ligase preparations from wild‐type or acc1 muttant cells. By the use of these mutants, evidence was obtained that in vivo the biotinylation of both acetyl‐CoA carboxylase and pyruvate carboxylase is catalyzed by the same ligase.