Rod-core linker protein required for attachment of rods with the core of the major allophycocyanins in phycobilisomes, plays a major role in light harvesting. Although able to transfer energy to both photosystems, this is predominantly a PSII antenna (PubMed:16049785, PubMed:17468217, PubMed:19152018). Involved in state transitions (PubMed:19152018). Part of the phycobilisome, a hemidiscoidal structure that is composed of two distinct substructures: a core complex and a number of rods radiating from the core. This protein is part of a conventional PBS rod (called CpcG-PBS) with on average 3 stacked phycocyanin hexamers (PC, CpcA and CpcB). Linker CpcG connects the PC stack to the thylakoid, the hexamers are linked by 1 copy of CpcC1, 1 copy of CpcC2 and the stack is terminated by a single copy of CpcD. Ferredoxin--NADP reductase (petH) is also part of the complex. The phycobilisome supercomplex detaches from the thylakoid easily. Decreased growth rate, decreased energy transfer to photosystem II. Decreased accumulation of phycocyanin (PC), loss of the phycobilisome supercomplex and major phycobiliproteins ApcE and allophycocyanin. A double cpcG1/cpcG2 deletion has even less PC, but grows slightly better than this single mutant (PubMed:16049785, PubMed:17468217). Unable to perform state 2 to state 1 transitions (i.e. cannot transfer energy to PSII) (PubMed:19152018). Belongs to the phycobilisome linker protein family. Extended N-terminus.