Question: What are phycobiliproteins and what role do they play in cyanobacteria and algae?

Context:
 "The amino acid sequences deduced from both rpeA and rpeB present strong homologies with those previously reported for phycoerythrin subunits of cyanobacteria, rhodophyta, and cryptomonads", "These transcripts are present in RNA isolated from cultures grown in red and green light, although lower levels of the 1600-base phycocyanin transcript are present in cells grown in green light", "Phycocyanin is a major protein produced by cyanobacteria, but very few phycocyanin-producing strains have been reported", "The major light-harvesting complex in eukaryotic red algae and prokaryotic cyanobacteria is the phycobilisome, a water-soluble complex located on the outer surface of the photosynthetic membranes and composed of both pigmented phycobiliproteins (85%) and non-pigmented linker (15%) polypeptides", "Phycocyanin--a major phycobiliprotein constitutively produced by many cyanobacteria--holds several promising applications in diagnostics, biomedical research, and therapeutics", "Phycobilisomes, the major light-harvesting complexes of cyanobacteria are multimolecular structures made up of chromophoric proteins called phycobiliproteins and non chromophoric linker polypeptides"]
["An extensive range of pigments including phycobiliproteins are present in algae. C-phycocyanin (C-PC), a phycobiliprotein, is one of the key pigments of Spirulina", "Spirulina platensis produces nutraceutical product C-phycocyanin (C-PC)", "C-Phycocyanin (C-Pc) is one of the major biliprotein pigments of unicellular cyanbacterium of Spirulina platenesis", "Marine Synechococcus owe their specific vivid color (ranging from blue-green to orange) to their large extrinsic antenna complexes called phycobilisomes, comprising a central allophycocyanin core and rods of variable phycobiliprotein composition.", "Three major pigment types can be defined depending on the major phycobiliprotein found in the rods (phycocyanin, phycoerythrin I or phycoerythrin II)", "Phycocyanin--a major phycobiliprotein constitutively produced by many cyanobacteria--", "R-phycoerythrin was isolated and purified from a red alga, Polysiphonia urceolata Grev", "C-phycocyanin (C-PC), one of the major phycobiliproteins of Spirulina platensis (a blue-green alga)", "C-Phycocyanin (C-PC), the major light harvesting biliprotein from Spirulina platensis is of greater importance because of its various biological and pharmacological properties.", "B-Phycoerythrin (B-PE) is a major light-harvesting pigment of microalgae.", "Phycoerythrin is a major light-harvesting pigment of red algae and cyanobacteria that is widely used as a fluorescent probe and analytical reagent. In this paper, B-phycoerythrin and R-phycocyanin in native state, from the red alga Porphyridium cruentum were obtained by an inexpensive and simple process.", "Phycobiliproteins are derived from the photosynthetic apparatus of cyanobacteria and eukaryotic algae.", "the three major phycobiliprotein types, namely allophycocyanin, phycocyanin, and phycoerythrin", "Phycoerythrin is a major light-harvesting pigment of red algae and cyanobacteria widely used as a fluorescent probe.", "allophycocyanin (APC)", "R-phycoerythrin is the major light-harvesting pigment protein of most red algal phycobilisomes.", "The purified protein had three absorption peaks at 498, 535, and 565 nm and displayed a fluorescence maximum at 580 nm, which was consistent with the typical spectrum of R-phycoerythrin. The purified R-PE was also identified with electrophoresis.", "Phycobilisomes, the major light-harvesting complexes of cyanobacteria are multimolecular structures made up of chromophoric proteins called phycobiliproteins and non chromophoric linker polypeptides.", "We report here the isolation and nucleotide sequence of the genes, cpeA and cpeB, which in Calothrix PCC 7601 encode the alpha and beta subunits of phycoerythrin, one of the major phycobiliproteins.", "The major light-harvesting complex in eukaryotic red algae and prokaryotic cyanobacteria is the phycobilisome, a water-soluble complex located on the outer surface of the photosynthetic membranes and composed of both pigmented phycobiliproteins (85%) and non-pigmented linker (15%) polypeptides.", "Phycocyanin is a major protein produced by cyanobacteria, but very few phycocyanin-producing strains have been reported.", "In the present work, phycocyanin (PC) and phycoerythrin (PE) from a Nostoc species are proposed as protein markers for electrophoretic techniques.", "Rod structure of a phycoerythrin II-containing phycobilisome. I. Organization and sequence of the gene cluster encoding the major phycobiliprotein rod components in the genome of marine Synechococcus sp. WH8020.", "We now present data showing that the allophycocyanin genes and a second set of phycocyanin genes are transcribed into major mRNAs of 1400 and 1600 bases, respectively",

Answer: Phycobiliproteins are pigmented proteins found in cyanobacteria and algae that are part of the photosynthetic apparatus. They play a crucial role in light harvesting and energy transfer processes in these organisms. Phycobiliproteins include phycocyanin, phycoerythrin, and allophycocyanin, among others, and are essential for efficient photosynthesis in cyanobacteria and algae.