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J. Bacteriol., 02 1997, 998-1006, Vol 179, No. 4
K Kahn, D Mazel, J Houmard, N Tandeau de Marsac and MR Schaefer
Pigment mutant strain FdR1 of the filamentous cyanobacterium Fremyella
diplosiphon is characterized by constitutive synthesis of the
phycobiliprotein phycoerythrin due to insertional inactivation of the rcaC
regulatory gene by endogenous transposon Tn5469. Whereas the parental
strain Fd33 harbors five genomic copies of Tn5469, cells of strain FdR1
harbor six genomic copies of the element; the sixth copy in FdR1 is
localized to the rcaC gene. Electroporation of FdR1 cells yielded secondary
pigment mutant strains FdR1E1 and FdR1E4, which identically exhibited the
FdR1 phenotype with significantly reduced levels of phycoerythrin. In both
FdR1E1 and FdR1E4, a seventh genomic copy of Tn5469 was localized to the
cpeY gene of the sequenced but phenotypically uncharacterized cpeYZ gene
set. This gene set is located downstream of the cpeBA operon which encodes
the alpha and beta subunits of phycoerythrin. Complementation experiments
correlated cpeYZ activity to the phenotype of strains FdR1E1 and FdR1E4.
The predicted CpeY and CpeZ proteins share significant sequence identity
with the products of homologous cpeY and cpeZ genes reported for
Pseudanabaena sp. strain PCC 7409 and Synechococcus sp. strain WH 8020,
both of which synthesize phycoerythrin. The CpeY and CpeZ proteins belong
to a family of structurally related cyanobacterial proteins that includes
the subunits of the CpcE/CpcF phycocyanin alpha-subunit lyase of
Synechococcus sp. strain PCC 7002 and the subunits of the PecE/PecF
phycoerythrocyanin alpha-subunit lyase of Anabaena sp. strain PCC 7120.
Phycobilisomes isolated from mutant strains FdR1E1 and FdR1E4 contained
equal amounts of chromophorylated alpha and beta subunits of phycoerythrin
at 46% of the levels of the parental strain FdR1. These results suggest
that the cpeYZ gene products function in phycoerythrin synthesis, possibly
as a lyase involved in the attachment of phycoerythrobilin to the alpha or
beta subunit.
Copyright © 1997, American Society for Microbiology
A role for cpeYZ in cyanobacterial phycoerythrin biosynthesis
School of Biological Sciences, University of Missouri-Kansas City, 64110, USA.
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