Three C-phycoerythrin-associated linker polypeptides in the phycobilisome of green-light-grown Calothrix sp. PCC 7601 (cyanobacteria)

Microanalyses by SDS-PAGE and microsequencing demonstrate that, under green-light conditions, 3 C-phycoerythrin associated rod-linker polypeptides with different N-terminal amino acid sequences are present in phycobilisomes (PBS) from Calothrix sp. 7601 cells. Two of these polypeptides, corresponding to SDS-PAGE bands at 36 and 37 kDa, could be assigned, respectively, to the cpeC and epeD genes found on a separate cpeCD-operon in Calothrix sp. 7601 (Federspiel, N.A. and Grossman, A.R. (1990) J. Bacteriol. 172, 4072-4081). The third C-PE rod-linker polypeptide, L_R,2^PE,33, requires, therefore, a third gene with the suggested locus designation 'cpeE'. A C-PE (αβ)₆-L_R,2^PE,33 complex containing this third rod-linker polypeptide could be isolated from phycobilisomes and characterized. PBS from both green- and red-light cells of Calothrix contain a single, unique L_RC²⁸ rod-core linker polypeptide which is not altered during chromatic adaptation.