Genes for phycocyanin subunits in Synechocystis sp. strain PCC 6701 and assembly mutant UV16

Abstract

The cyanobacterial phycobilisome is a large protein complex located on the photosynthetic membrane. It harvests light energy and transfers it to chlorophyll for use in photosynthesis. Phycobilisome assembly mutants in the unicellular cyanobacterium Synechocystis sp. strain 6701 have been characterized. One such mutant, UV16, contains a defect in the assembly of the biliprotein phycocyanin. We report the cloning and sequencing of the phycocyanin genes from wild-type Synechocystis strain 6701 and demonstrate an alteration in the gene for the phycocyanin a subunit in UV16. Possible consequences of the lesion on phycobilisome assembly were assessed from its position in the phycocyanin tertiary and quaternary structures. The UV16 phenotype is complex and includes a reduced level of phycocyanin relative to that in the wild type. To determine whether the lower phycocyanin content results from lower transcript levels, a fragment of cpcBA was used as a probe for quantitating phycocyanin mRNA. Both the wild type and UV16 contained two phycocyanin transcripts of approximately 1.4 and 1.5 kilobases that were equal in abundance and that did not vary with light quality during cell growth. Equal levels of these transcripts in the wild type and UV16 suggest that the lower phycocyanin content in the mutant may be due to posttranscriptional events. The 5' ends of the two phycocyanin mRNAs were mapped at 100 and 223 base pairs upstream of the cpcB initiation codon. Homologous regions upstream of the putative transcription initiation sites may be important for maintaining high levels of transcription from the Synechocystis strain 6701 phycocyanin gene set.

Structure and light-regulated expression of phycoerythrin genes in wild-type and phycobilisome assembly mutants of Synechocystis sp. strain PCC 6701

“…This observation suggests that posttranscriptional processes may be important in establishing PE levels in Analysis of PE genes in a phycoerythrin assembly mutant. One approach to studying phycobilisome structure and assembly has involved the analysis of UV-induced phycobilisome assembly mutants in Synechocystis strain 6701 (2)(3)(4). The UV16 mutant is defective in PC assembly, but it also exhibits other aberrant characteristics such as decreased levels of PE (55% that of the WT) and an abnormal response to red light during chromatic adaptation.…”

“…Mutagenesis of UV16 resulted in the UV16-40 that is defective in both PC and PE assembly (4). Cyanobacteria were grown as previously described (2). The Escherichia coli strains used in this study were JM101, for M13 cloning and the isolation of sequencing templates (31) (26), and the Sau3AI ends were partially filled in with A and G residues by using the Klenow fragment of DNA polymerase I.…”

“…Clones containing part of cpeB were used as hybridization probes to screen the library to obtain DNA fragments containing the complete PE gene set, cpeBA. The isolated genes were sequenced as previously described (2). The UV16-40 PE genes were amplified by the polymerase chain reaction (PCR) by using primers (see Fig.…”

The complete amino acid sequence of R‐phycocyanin‐I α and β subunits from the red alga Porphyridium cruentum

“…a-C-PE a-C-PE a-B-PE a-B-PE a-C-PE a-B-PE a-PE-I1 a-PE a-PEC a-PEC a-R-PC-I a-R-PC-I1 a-C-PC-I a-C-PC-I1 a-C-PC-111 a-C-PC a-C-PC Anderson andGrossman (1990) Fiiglistaller et al (1983), Eberlein and Kufer (1990) Swanson et al (1992) this work, submitted to data banks (1994) De Lorimier et al (1993, Conley et al (1988) Capuano et al (1988), Conley et al (1988, Mazel and Marliere (1989) Belknap andHaselkorn (1987) Offner et al (1981) Frank et al (1978), Kufer, W., Hoenger, A., Eberlein, M., Mayer, K.,…”

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