CpeR is an activator required for expression of the phycoerythrin operon (cpeBA) in the cyanobacterium Fremyella diplosiphon and is encoded in the phycoerythrin linker-polypeptide operon (cpeCDESTR).
In the cyanobacteria, phycobilisomes are assembled from (alphabeta)(6) hexamers of the coloured phycobiliproteins, allophycocyanin, phycocyanin and phycoerythrin (PE). The precise architecture of the phycobilisome is determined by the various colourless linker proteins that bind to the biliprotein hexamers. Genes for beta and alpha subunits of PE make up one operon (cpeBA), whereas genes for PE-associated linker polypeptides are in a second operon. In the chromatically adapting cyanobacterium Fremyella diplosiphon green light is required for the transcription of both cpeBA and the operon encoding the PE-associated linkers (cpeCDE). From the genome of F. diplosiphon we have identified an open reading frame, cpeR, which, when expressed from a shuttle plasmid, is capable of suppressing various mutations that cause a decrease in PE synthesis. The introduction of a shuttle plasmid bearing cpeR+ into wild-type F. diplosiphon caused PE expression in red light. Fremyella diplosiphon cpeR-, created by in vitro mutagenesis and in vivo homologous recombination, is fully PE and, in this strain, cpeCDE is transcribed normally whereas the transcript from cpeBA is undetectable. Polymerase chain reaction (PCR) amplification of cDNA showed that cpeR is transcribed as part of the cpeCDE operon on an extended transcript. As CpeR is an activator required for expression of the cpeBA operon, we propose that at the onset of green light the operons cpeCDESTR and cpeBA are expressed in series as a genetic cascade.
Cobley
John G
JG
Department of Chemistry, University of San Francisco, San Francisco, CA 94117, USA. cobley@usfca.edu
Clark
A Clay
AC
Weerasurya
Siromi
S
Queseda
F Anne
FA
Xiao
Jimmy Y
JY
Bandrapali
Nirmala
N
D'Silva
Ian
I
Thounaojam
Maya
M
Oda
Jeffrey F
JF
Sumiyoshi
Teiko
T
Chu
Man-Ho
MH
D001426:Bacterial Proteins / Q000235:genetics / Q000502:physiology*; D015152:Blotting, Northern; D003001:Cloning, Molecular; D003360:Cosmids; D000458:Cyanobacteria / Q000235:genetics* / Q000378:metabolism; D004926:Escherichia coli / Q000235:genetics; D015964:Gene Expression Regulation, Bacterial / Q000528:radiation effects; D015723:Gene Library; D008027:Light; D045342:Light-Harvesting Protein Complexes; D008969:Molecular Sequence Data; D009876:Operon; D045524:Phycobilisomes; D010799:Phycoerythrin / Q000096:biosynthesis / Q000235:genetics*; D010860:Pigments, Biological / Q000235:genetics / Q000378:metabolism; D011506:Proteins; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014158:Transcription, Genetic
D001426:Bacterial Proteins; C449644:CpeR protein, Fremyella diplosiphon; D045342:Light-Harvesting Protein Complexes; D045524:Phycobilisomes; D010860:Pigments, Biological; D011506:Proteins; D010799:Phycoerythrin; C076612:CpeE protein, Fremyella diplosiphon