THE AGMENELLUM QUADRUPLICATUM C-PHYCOCYANIN GENES: CLONING, SEQUENCING, AND CHARACTERIZATION (OLIGONUCLEOTIDE PROBE, BLUE-GREEN ALGAE, PHYCOBILIPROTEINS)

Synthetic oligonucleotide probes were used to identify a cloned DNA fragment from the cyanobacterium Agmenellum quadruplicatum that contains the genes for the alpha and beta subunits of C-phycocyanin. The coding region for the alpha subunit gene begins 108 base pairs downstream from the 3' end of the beta subunit gene. The sequences of the coding regions for both genes have been determined as well as 379 base pairs of 5' flanking region, 204 base pairs of 3' flanking region, and the 108 base pairs between the two genes. The site of transcriptional initiation is located approximately 325 base pairs upstream from the beta gene, and an open reading frame 114 base pairs in length is found within this region. It is not known whether this open reading frame is translated in vivo, nor what the function of this putative polypeptide may be. Both the C-phycocyanin alpha and beta genes are located on a single messenger RNA transcript and there is a single copy of the coding region for these genes within Agmenellum quadruplicatum, located on the chromosome.;The derived amino acid sequences for both Agmenellum quadruplicatum C-phycocyanin subunits were compared with other known C-phycocyanin sequences for homology. Homologies between the Agmenellum quadruplicatum alpha subunit and alpha subunits from other species were around 70%, as were the homologies between the Agmenellum quadruplicatum beta subunit and other beta subunits. Homologies between the various alpha and beta subunits were 21 to 27%. Codon usage for both the C-phycocyanin alpha and beta genes shows asymmetries for many amino acids that correspond closely to those seen in highly expressed E. coli genes.