Primary structure of the multifunctional alpha subunit protein of yeast fatty acid synthase derived from FAS2 gene sequence

Abstract

The yeast fatty acid synthase consists of two multifunctional proteins, alpha and beta, arranged in an alpha 6 beta 6 complex with a molecular weight of 2.4 x 10(6). Five of the seven enzymatic activities reside in the beta subunit, while the remaining two activities, beta-ketoacyl synthase and beta-ketoacyl reductase, and the domain of the acyl carrier protein, with its prosthetic group, 4'-phosphopantetheine, are in the alpha subunit. The genes FAS1 and FAS2 coding for beta and alpha subunits, respectively, have been cloned and the sequence of FAS1 has been reported (Chirala, S. S., Kuziora, M. A., Spector, D. M., and Wakil, S. J. (1987) J. Biol. Chem. 262, 4231-4240). In this study, we present the nucleotide sequence of the FAS2 gene. The sequence has an open reading frame, coding for a protein of 1894 amino acids with a calculated molecular weight of 207,863. The location of the serine site of attachment of the prosthetic group of the acyl carrier protein domain and the active cysteine-SH site of beta-ketoacyl synthase have been identified at residues 180 and 1312, respectively, in the deduced amino acid sequence. A putative NADPH binding site of beta-ketoacyl reductase has been suggested at residue 1038 based on the similarities to the consensus amino acid sequences -Gly-Ser-Ala- of the pyridine nucleotide enzymes. We could not find any sequence homology in the 5' flanking sequence of the FAS1 and FAS2 genes that would suggest common regulatory function. However, in the sequence of these two genes there is an identical eight-base pair sequence TCATTATG at the translational initiation site suggesting that the subunit stoichiometry probably results from equal translational efficiency of the mRNAs of both FAS1 and FAS2 genes. The S1 endonuclease mapping suggests that there is a transcriptional initiation site at about 40 nucleotides upstream of the first ATG codon and a transcriptional termination site about 300 nucleotides downstream of the TAG stop codon. The gene does not contain introns as no intron consensus TACTAAC have been found in the sequence.