Soitamo A J, Zhou G, Clarke A K, Oquist G, Gustafsson P, Aro E M
Dept. of Biology, University of Turku, Finland.
Plant Mol Biol. 1996 Feb;30(3):467-78. doi: 10.1007/BF00049325.
Over-expression of the psbAIII gene encoding for the D1 protein (form II; D1:2) of the photosystem II reaction centre in the Synechococcus sp. PCC 7942 was studied using a tac promoter and the lacIQ system. Over-expression was induced with 40 microgram/ml IPTG in the growth medium for either 6 or 12 h at growth irradiance (50 mumol photons m-2 s-1). This treatment doubled the amount of psbAII/III mRNA and the D1:2 protein in membranes but decreased the amount of psbAI messages and the D1:1 protein. The total amount of both heterodimeric reaction centre proteins, D1 and D2, remained constant under growth light conditions, indicating that the number of PSII centres in the membranes was not affected, only the form of the D1 protein was changed from D1:1 to D1:2 in most centres. When the cells were photoinhibited either at 500 or 1000 mumol photons m-2 s-1, in the presence or absence of the protein synthesis inhibitor lincomycin, the D1:2 protein remained at a higher level in cells in which over-expression had been induced by IPTG. These cells were also less prone to photoinhibition of PSII. It is suggested that the tolerance of cells to photoinhibition increases when most PSII reaction centres contain the D1:2 protein at the beginning of high irradiance. This tolerance is further strengthened by maintaining psbAIII gene over-expression during the photoinhibitory treatment.
利用tac启动子和lacIQ系统，研究了聚球藻属PCC 7942中光系统II反应中心编码D1蛋白（II型；D1:2）的psbAIII基因的过表达情况。在生长辐照度（50 μmol光子·m⁻²·s⁻¹）下，于生长培养基中加入40 μg/ml异丙基-β-D-硫代半乳糖苷（IPTG）诱导过表达6或12小时。该处理使膜中psbAII/III mRNA和D1:2蛋白的量增加了一倍，但减少了psbAI信息和D1:1蛋白的量。在生长光照条件下，两种异二聚体反应中心蛋白D1和D2的总量保持恒定，这表明膜中PSII中心的数量未受影响，只是在大多数中心，D1蛋白的形式从D1:1变为了D1:2。当细胞在500或1000 μmol光子·m⁻²·s⁻¹下进行光抑制处理时，无论有无蛋白质合成抑制剂林可霉素，在经IPTG诱导过表达的细胞中，D1:2蛋白水平仍较高。这些细胞对PSII光抑制也更具抗性。研究表明，当大多数PSII反应中心在高辐照度开始时含有D1:2蛋白时，细胞对光抑制的耐受性会增加。在光抑制处理期间维持psbAIII基因的过表达可进一步增强这种耐受性。
