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J. Bacteriol., 08 1996, 4787-4793, Vol 178, No. 16
HP Stuible, C Wagner, I Andreou, G Huter, J Haselmann and E Schweizer
The fatty acid synthase (FAS) from Brevibacterium ammoniagenes is a
homohexameric multienzyme complex that catalyzes the synthesis of both
saturated and unsaturated fatty acids. By immunological screening of a B.
ammoniagenes expression library, an fas DNA fragment was isolated and
subsequently used to clone the entire gene together with its flanking
sequences. Within 10,525 bp of sequenced DNA, the 9,189-bp FAS coding
region was identified, corresponding to a protein of 3,063 amino acids with
a molecular mass of 324,910 Da. This gene (fasA) encodes, at its 5' end,
the same amino acid sequence as is observed with purified B. ammoniagenes
FAS. A second reading frame encoding another B. ammoniagenes FAS variant
(FasB) had been identified previously. Both sequences are colinear and
exhibit 61 and 47% identity at the DNA and protein levels, respectively. By
using specific antibodies raised against a unique peptide sequence of FasB,
this enzyme was shown to represent only 5 to 10% of the cellular FAS
protein. Insertional inactivation of the FasB coding sequence causes no
defective phenotype, while fasA disruptants require oleic acid for growth.
Correspondingly, oleate-dependent B. ammoniagenes cells obtained by ethyl
methanesulfonate mutagenesis were complemented by transformation with fasA
DNA but not with fasB DNA. The data indicate that B. ammoniagenes contains
two related though differently expressed type I FASs. FasA represents the
bulk of cellular FAS protein and catalyzes the synthesis of both saturated
and unsaturated fatty acids, while the minor variant, FasB, cannot catalyze
the synthesis of oleic acid.
Copyright © 1996, American Society for Microbiology
Identification and functional differentiation of two type I fatty acid synthases in Brevibacterium ammoniagenes
Lehrstuhl fur Biochemie der Universitat Erlangen-Nurnberg, Germany.
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