Kahn K, Mazel D, Houmard J, Tandeau de Marsac N, Schaefer M R
School of Biological Sciences, University of Missouri-Kansas City, 64110, USA.
J Bacteriol. 1997 Feb;179(4):998-1006. doi: 10.1128/jb.179.4.998-1006.1997.
Pigment mutant strain FdR1 of the filamentous cyanobacterium Fremyella diplosiphon is characterized by constitutive synthesis of the phycobiliprotein phycoerythrin due to insertional inactivation of the rcaC regulatory gene by endogenous transposon Tn5469. Whereas the parental strain Fd33 harbors five genomic copies of Tn5469, cells of strain FdR1 harbor six genomic copies of the element; the sixth copy in FdR1 is localized to the rcaC gene. Electroporation of FdR1 cells yielded secondary pigment mutant strains FdR1E1 and FdR1E4, which identically exhibited the FdR1 phenotype with significantly reduced levels of phycoerythrin. In both FdR1E1 and FdR1E4, a seventh genomic copy of Tn5469 was localized to the cpeY gene of the sequenced but phenotypically uncharacterized cpeYZ gene set. This gene set is located downstream of the cpeBA operon which encodes the alpha and beta subunits of phycoerythrin. Complementation experiments correlated cpeYZ activity to the phenotype of strains FdR1E1 and FdR1E4. The predicted CpeY and CpeZ proteins share significant sequence identity with the products of homologous cpeY and cpeZ genes reported for Pseudanabaena sp. strain PCC 7409 and Synechococcus sp. strain WH 8020, both of which synthesize phycoerythrin. The CpeY and CpeZ proteins belong to a family of structurally related cyanobacterial proteins that includes the subunits of the CpcE/CpcF phycocyanin alpha-subunit lyase of Synechococcus sp. strain PCC 7002 and the subunits of the PecE/PecF phycoerythrocyanin alpha-subunit lyase of Anabaena sp. strain PCC 7120. Phycobilisomes isolated from mutant strains FdR1E1 and FdR1E4 contained equal amounts of chromophorylated alpha and beta subunits of phycoerythrin at 46% of the levels of the parental strain FdR1. These results suggest that the cpeYZ gene products function in phycoerythrin synthesis, possibly as a lyase involved in the attachment of phycoerythrobilin to the alpha or beta subunit.
丝状蓝细菌双岐藻弗氏藻（Fremyella diplosiphon）的色素突变株FdR1的特征是，由于内源性转座子Tn5469插入使rcaC调控基因失活，藻胆蛋白藻红蛋白组成型合成。亲本菌株Fd33含有5个Tn5469基因组拷贝，而FdR1菌株的细胞含有该元件的6个基因组拷贝；FdR1中的第6个拷贝定位于rcaC基因。对FdR1细胞进行电穿孔产生了次级色素突变株FdR1E1和FdR1E4，它们同样表现出FdR1表型，藻红蛋白水平显著降低。在FdR1E1和FdR1E4中，Tn5469的第7个基因组拷贝定位于已测序但表型未鉴定的cpeYZ基因集的cpeY基因。该基因集位于编码藻红蛋白α和β亚基的cpeBA操纵子下游。互补实验将cpeYZ活性与FdR1E1和FdR1E4菌株的表型相关联。预测的CpeY和CpeZ蛋白与报道的假鱼腥藻（Pseudanabaena sp.）菌株PCC 7409和聚球藻（Synechococcus sp.）菌株WH 8020的同源cpeY和cpeZ基因产物具有显著的序列同一性，这两种菌株都合成藻红蛋白。CpeY和CpeZ蛋白属于一类结构相关的蓝细菌蛋白家族，该家族包括聚球藻菌株PCC 7002的CpcE/CpcF藻蓝蛋白α亚基裂合酶的亚基以及鱼腥藻菌株PCC 7120的PecE/PecF藻红青蛋白α亚基裂合酶的亚基。从突变株FdR1E1和FdR1E4分离的藻胆体含有等量的藻红蛋白的磷酸化α和β亚基，其含量为亲本菌株FdR1水平的46%。这些结果表明，cpeYZ基因产物在藻红蛋白合成中起作用，可能作为一种参与藻红胆素与α或β亚基连接的裂合酶。
