Su X, Fraenkel P G, Bogorad L
Biological Laboratories, Harvard University, Cambridge, Massachusetts 02138.
J Biol Chem. 1992 Nov 15;267(32):22944-50.
A greenish mutant of the normally blue-green cyanobacterium Synechocystis sp. PCC 6803, designated UV6p, has been isolated and characterized. UV6p possesses functional photosystems I and II (PSI and PSII) but lacks normal light harvesting phycobilisomes because allophycocyanin is absent and core-specific linker proteins are almost entirely absent. The mutation responsible for the UV6p phenotype has been identified; it is a base substitution which results in the creation of a termination codon within the coding region of the apcA gene. Phycocyanin (PC) and phycobilisome rod linker proteins are present in UV6p and, despite the absence of core components, at least 35% of the PC is associated with rod linker proteins. At 77 K, light absorbed by PC of UV6p elicits PSI fluorescence comparable to that of wild type cells but produces greatly diminished PSII fluorescence. The results indicate that the assembly of rods is independent of cores and that light energy absorbed by rods can be transferred principally and directly to PSI. This energy transfer pathway, which may also be present in wild type, may have a regulatory role in maintaining the balance of input of excitation energy into PSI versus PSII during photosynthesis.
已分离并鉴定出正常蓝绿色集胞藻属PCC 6803的一种绿色突变体，命名为UV6p。UV6p具有功能性的光系统I和II（PSI和PSII），但缺乏正常的捕光藻胆体，因为别藻蓝蛋白缺失且核心特异性连接蛋白几乎完全缺失。已鉴定出导致UV6p表型的突变；它是一个碱基替换，导致在apcA基因编码区内产生一个终止密码子。藻蓝蛋白（PC）和藻胆体杆状连接蛋白存在于UV6p中，尽管缺乏核心成分，但至少35%的PC与杆状连接蛋白相关。在77 K时，UV6p的PC吸收的光引发的PSI荧光与野生型细胞相当，但产生的PSII荧光大大减弱。结果表明，杆状结构的组装独立于核心结构，并且杆状结构吸收的光能可以主要且直接地转移到PSI。这种能量转移途径可能也存在于野生型中，在光合作用期间维持激发能输入到PSI与PSII的平衡方面可能具有调节作用。
