Alpha subunit of fatty acid synthetase (FAS); the FAS complex catalyzes the synthesis of long-chain saturated fatty acids and is subject to allosteric regulation by palmitoyl-CoA binding distal to the catalytic site to inhibit ketoacyl reductase activity; contains the acyl-carrier protein domain and beta-ketoacyl reductase, beta-ketoacyl synthase and self-pantetheinylation activities