Rod linker protein, associated with phycocyanin (PC). Linker polypeptides determine the state of aggregation and the location of the disk-shaped phycobiliprotein units within the phycobilisome (PBS) and modulate their spectroscopic properties in order to mediate a directed and optimal energy transfer. Forms a supercomplex with tetrameric photosystem I (PSI) and PC that allows efficient energy transfer from PC to PSI. This protein seems to be in the middle of the PC hexameric rod and may anchor the PC rods at the periphery of PSI tetramers. May be involved in the cyclic electron transport around PSI that provides ATP needed for N(2) fixation in heterocysts (PubMed:24550276). Part of a specialized phycobilisome (PBS), a structure that is usually composed of two distinct substructures: a core complex and a number of rods radiating from the core. This protein is part of a core-less PBS rod (called CpcL-PBS). In vegetative cells associated substoichiometrically with photosystem I and phycobiliproteins phycocyanin as well as phycoerythrocyanin in the thylakoid membrane, not found in conventional, hemidiscoidal phycobilisomes. Part of a core-less phycobilisome rod (CpcL-PBS). A portion of the protein is not associated with thylakoids in N(2)-fixing heterocysts. Expressed in both vegetative cells and in N(2)-fixing heterocysts; considerably more abundant in heterocysts (at protein level). Belongs to the phycobilisome linker protein family.