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Mol. Cell. Biol., 01 1995, 264-271, Vol 15, No. 1
M Wu, B Repetto, DM Glerum and A Tzagoloff
The FAD1 gene of Saccharomyces cerevisiae has been selected from a genomic
library on the basis of its ability to partially correct the respiratory
defect of pet mutants previously assigned to complementation group G178.
Mutants in this group display a reduced level of flavin adenine
dinucleotide (FAD) and an increased level of flavin mononucleotide (FMN) in
mitochondria. The restoration of respiratory capability by FAD1 is shown to
be due to extragenic suppression. FAD1 codes for an essential yeast
protein, since disruption of the gene induces a lethal phenotype. The FAD1
product has been inferred to be yeast FAD synthetase, an enzyme that
adenylates FMN to FAD. This conclusion is based on the following evidence.
S. cerevisiae transformed with FAD1 on a multicopy plasmid displays an
increase in FAD synthetase activity. This is also true when the gene is
expressed in Escherichia coli. Lastly, the FAD1 product exhibits low but
significant primary sequence similarity to sulfate adenyltransferase, which
catalyzes a transfer reaction analogous to that of FAD synthetase. The
lower mitochondrial concentration of FAD in G178 mutants is proposed to be
caused by an inefficient exchange of external FAD for internal FMN. This is
supported by the absence of FAD synthetase activity in yeast mitochondria
and the presence of both extramitochondrial and mitochondrial riboflavin
kinase, the preceding enzyme in the biosynthetic pathway. A lesion in
mitochondrial import of FAD would account for the higher concentration of
mitochondrial FMN in the mutant if the transport is catalyzed by an
exchange carrier.(ABSTRACT TRUNCATED AT 250 WORDS)
Copyright © 1995, American Society for Microbiology
Cloning and characterization of FAD1, the structural gene for flavin adenine dinucleotide synthetase of Saccharomyces cerevisiae
Department of Biological Sciences, Columbia University, New York, New York 10027.
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