Characterization of a light-regulated gene encoding a new phycoerythrin-associated linker protein from the cyanobacterium Fremyella diplosiphon

Abstract

Cyanobacteria utilize multimeric protein complexes, the phycobilisomes, as their maljor light-harvesting antennae. Associated with the chromophorylated phycobiliproteins in these complexes are nonpigmented proteins, designated linker proteins. These linker proteins are believed to mediate assembly of the phycobilisome and energy transfer to the photosynthetic reaction center. We cloned and sequenced a gene, cpeE, encoding a previously uncharacterized linker protein which is expressed in green light in Fremyella diplosiphon. This gene is part of an operon containing two other phycoerythrin-associated linker genes, cpeC and cpeD. Transcription of the cpeCDE operon in green light results in two predominant species of mRNA of -2,100 and 3,200 nucleotides. The shorter transcript encodes only CpeC and CpeD, while the longer contains the coding regions for all three linker proteins. By altering the pH of the resolving gel and the rnmning buffer during sodium dodecyl sulfate-polyacrylamide gel electrophoresis, this third linker protein CpeE can be resolved from the rod-core linker and the other rod linker proteins. The three proteins have an overall similarity of -62%, and the genes encoding the three proteins are -59%o identical.

Tracking the Light Environment by Cyanobacteria and the Dynamic Nature of Light Harvesting

“…In contrast to the situation for cpc and apc operons, genes encoding L polypeptides associated with PE are not contiguous on the genome to cpeBA; they are encoded by the cpeCDE operon (16). However, GL activation and RL suppression of cpeBA and cpeCDE are coordinated.…”

Rhodopsin(s) in eubacteria

“…5). The genes involved in this adaptive response have been mapped and the information available on gene activation occurring in CCA [19], including phosphorylation-dependent binding of an activator protein in the promoter region of genes encoding antenna polypeptides [20], suggests the involvement of a two-component signal transduction system, for which a sensor protein has been identified via complementation analysis of CCA-deficient mutants [21]. The protein identified in this complementation, RcaC, shows similarities with other sensor proteins of the two-component family [22].…”

A molecular understanding of complementary chromatic adaptation

“…Furthermore, genes encoding the linker polypeptides associated with PC i , cpcHID, are RL-inducible and co-transcribed with cpcB2A2 (Lomax et al 1987). And while genes encoding the linker polypeptides associated with PE, cpeCDE, are also under the control of RL and GL, they are not in the same operon as cpeBA (Federspiel and Grossman 1990;Federspiel and Scott 1992). My laboratory was most interested in understanding the mechanisms controlling PBS gene expression and there were two viable approaches for defining regulators of this process; one approach involved using biochemical techniques to identify factors that associate with promoters of phycobiliprotein genes, whereas the other involved generating mutants with aberrant CCA and identifying genes altered in the mutant strains.…”