Here, we report the isolation of a mutant in F. diplosiphon that is chartreuse (FdCh) in color. This mutant contains a disrupted cpcF gene and provides a genetic tool for investigating the role of CpcF in F. diplosiphon in greater detail than previously reported. cpcE and cpcF genes encode enzymes central to PC biosynthesis in
FLAG Peptide [13]. It was determined previously that cpcE is co-transcribed with PC apoprotein-encoding genes cpcB1 and cpcA1 in F. diplosiphon; however, cpcF reportedly is transcribed as a monocistronic message [32]. Initial reports suggested that a cpcF mutant is defective in PCi accumulation in RL specifically due to a defect in chromophore attachment to the α subunit of PC [33]. A cpcF mutant also was described as defective in accumulating PE in GL conditions [31] and [32] and as lacking constitutive PC (PCc), which is present in both RL and GL conditions, as well [32]. The PBSs isolated from this cpcF mutant were reported to be smaller in size than those isolated from WT
cells [32]. The pleiotropic phenotype of the cpcF mutant was hypothesized to reflect a regulatory role for chromophore molecules in the accumulation of PBPs and/or PBS synthesis [31] and [33]. In other cyanobacteria, including Synechococcus sp. PCC 7002 and Mastigocladus laminosus PCC 7603, CpcE and CpcF have been shown to operate as a heterodimeric lyase enzyme that catalyzes the attachment of the PCB chromophore to Cys-84 of the α subunit of PC, as well as catalyzing chromophore detachment and transfer [13], [14], [29] and [36]. In these non-PE-producing organisms, disruption of cpcE or cpcF resulted in a specific defect in PC accumulation [6], [29] and [37]. In Anaebaena sp. PCC 7120, which produces phycoerythrocyanin (PEC) in addition to PC, insertional mutagenesis of cpcE or cpcF resulted in a lack of PC accumulation, but notably an overproduction of PEC, particularly under low light conditions [10].
