Genomic and functional characterization of the oas gene family encoding O-acetylserine (thiol) lyases, enzymes catalyzing the final step in cysteine biosynthesis in Arabidopsis thaliana
R. Jost et al., Genomic and functional characterization of the oas gene family encoding O-acetylserine (thiol) lyases, enzymes catalyzing the final step in cysteine biosynthesis in Arabidopsis thaliana, GENE, 253(2), 2000, pp. 237-247
The final step of cysteine biosynthesis in plants is catalyzed by O-acetyls
erine (thiol) lyase (OAS-TL), which occurs as several isoforms found in the
cytosol, the plastids and the mitochondria. Genomic DNA blot hybridization
and isolation of genomic clones indicate single copy genes (oasA1, oasA2,
oasB and oasC) that encode the activities of OAS-TL A, B and C found in sep
arate subcellular compartments in the model plant Arabidopsis thaliana. Seq
uence analysis reveals that the newly discovered oasA2 gene represents a ps
eudogene that is still transcribed, but is not functionally translated. The
comparison of gene structures suggests that oasA1/oasA2 and oasB/oasC are
closely related and may be derived from a common ancestor by subsequent dup
lications. OAS-TL A, B and C were overexpressed in an Escherichia coli muta
nt lacking cysteine synthesis and exhibited bifunctional OAS-TL and beta-cy
anoalanine synthase (CAS) activities. However, all three proteins represent
true OAS-TLs according to kinetic analysis and are unlikely to function in
cyanide detoxification or secondary metabolism. In addition. it was demons
trated that the mitochondrial OAS-TL C exhibits in vivo protein-protein int
eraction capabilities with respect to cysteine synthase complex formation s
imilar to cytosolic OAS-TL A and plastid OAS-TL B. Multiple database access
ions for each of the A. thaliana OAS-TL isoforms can thus be attributed to
a specified number of oas genes to which functionally defined gene products
are assigned, and which art responsible for compartment-specific cysteine
synthesis. (C) 2000 Elsevier Science B.V. All rights reserved.