Volume 270,
Number 21,
Issue of May 26, pp. 12877-12884, 1995
©1995 by The American Society for Biochemistry and Molecular Biology, Inc.
Candidate
Genes for the Phycoerythrocyanin 
Subunit Lyase
BIOCHEMICAL ANALYSIS OF pecE AND pecF INTERPOSON
MUTANTS
Linda J. Jung, Crystal
F. Chan, and
Alexander N. Glazer
The rod substructures of the Anabaena sp. PCC 7120
phycobilisome contain the light harvesting proteins C-phycocyanin and
phycoerythrocyanin (PEC). Even at low light intensities, PEC represents
no more than 5% of the phycobilisome protein. The 
subunits of
both proteins carry thioether-linked phycocyanobilin (PCB) at
-Cys-82 and -Cys-155; however, C-phycocyanin has PCB at
-Cys-84 whereas PEC subunit carries phycobiliviolin at this
position. The Anabaena sp. PCC 7120 pec operon is
made up of five genes. PecB and pecA encode the
and subunits of PEC, pecC encodes a linker polypeptide
associated with PEC in the rod substructure, and pecE and
pecF are genes of unknown function that show a high degree of
homology to cpcE and cpcF, that encode a
C-phycocyanin subunit PCB lyase (Fairchild, C. D., Zhao, J.,
Zhou, J., Colson, S. E., Bryant, D. A., and Glazer, A. N.(1992)
Proc. Natl. Acad. Sci. U. S. A. 89,
7017-7021). Insertional mutants in pecE and
pecF, and an interposon mutant in which a portion of both
pecE and pecF was deleted, were constructed. All
three types of mutants grew 1.3 times slower than wild-type under
limiting light conditions and showed a 20% reduction in the PCB content
of whole cells relative to chlorophyll a. Holo-PEC was missing
from the phycobilisomes of all three types of mutants and the level of
the PEC linker polypeptide was reduced relative to the wild-type.
However, 
30% of the wild-type level of the PEC subunit was
present in all of these phycobilisomes. In contrast, the PEC
subunit was barely detectable in the pecE and pecF mutants, but was present in the pecEF deletion mutant as
a PCB-adduct in a 1:1 ratio with the PEC subunit. The identity of
this ``unnatural'' adduct was confirmed by isolation of the
subunit and amino-terminal sequencing. These biochemical results
support the inference that pecE and pecF encode a PEC
subunit phycobiliviolin lyase, and, in conjunction with earlier
findings, demonstrate that phycobiliprotein bilin lyases show high
selectivity (rather than absolute specificity) for both the bilin and
the polypeptide substrate.
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