Gleiter H M, Ohad N, Koike H, Hirschberg J, Renger G, Inoue Y
RIKEN, Institute of Physical and Chemical Research, Wako, Japan.
Biochim Biophys Acta. 1992 Dec 7;1140(2):135-43. doi: 10.1016/0005-2728(92)90002-j.
Several strains of Synechococcus PCC7942 carrying point mutations in the gene psbA were studied by thermoluminescence and polarographic measurement of flash-induced oxygen yield. The following results were obtained: (a) Replacement of Ser-264 in D1 by Ala (mutant Di1) or Gly (mutant G264) resulting in DCMU and atrazine resistance leads to a downshift of the thermoluminescence (TL) B-band peak temperature from 40 degrees C in wild-type thylakoids to about 30 degrees C. In dark adapted samples of both mutants the TL and oxygen yield pattern induced by a train of single turnover flashes were strongly damped indicative of a high miss factor. (b) In contrast to Ser-264 mutants, replacement of Phe-255 in D1 by Tyr (mutant Tyr5) induced strong resistance to atrazine but not to DCMU and did not affect the peak termperature of the B-band and the flash-induced TL and oxygen yield patterns. In this respect mutant Tyr5 resembles the wild type. (c) No significant differences have been found between strains with single site mutations in psbAI and normal psbAII/psbAIII genes, and strains with same mutations in psbAI but additional deletion of psbAII and psbAIII. Obviously in strains were psbAI is present, PS II complexes containing gene products of psbAII and psbAIII are not assembled in detectable amounts. (d) Strains with double mutations at positions 264 and 255 display a downshift of the B-band peak temperature. Their oscillatory patterns of B-band intensity and oxygen yield are highly damped. This behaviour is similar to strains D1 and G264 which are modified at position 264 only. We extend reports on additivity of mutation effects on herbicide binding to binding of QB. (e) Mutations at the QB site not only influence the binding of QB and herbicides but also change the thermoluminescence quantum yield and the lifetimes of the redox states S2 and S3 of the water oxidase. This finding might indicate long ranging effects on Photosystem II exerted by structural modifications of the QB site. From these data we conclude that Ser-264 is essential for binding of atrazine, DCMU and QB, whereas Phe-255 is involved in atrazine binding and its substitution by Tyr does not markedly affect QB or DCMU binding in Synechococcus PCC7942.
通过热发光以及对闪光诱导的氧气产量进行极谱测量，研究了集胞藻PCC7942中携带psbA基因突变的几个菌株。获得了以下结果：(a) D1中Ser-264被Ala（突变体Di1）或Gly（突变体G264）取代，导致对敌草隆（DCMU）和莠去津产生抗性，这使得热发光（TL）B带峰值温度从野生型类囊体中的40℃下移至约30℃。在这两个突变体的暗适应样品中，由一系列单次周转闪光诱导的TL和氧气产量模式受到强烈抑制，表明错配因子很高。(b) 与Ser-264突变体相反，D1中Phe-255被Tyr取代（突变体Tyr5）诱导出对莠去津的强抗性，但对DCMU没有抗性，并且不影响B带的峰值温度以及闪光诱导的TL和氧气产量模式。在这方面，突变体Tyr5类似于野生型。(c) 在psbAI中有单一位点突变的菌株与正常的psbAII/psbAIII基因，以及在psbAI中有相同突变但psbAII和psbAIII额外缺失的菌株之间，未发现显著差异。显然，在存在psbAI的菌株中，含有psbAII和psbAIII基因产物的PS II复合物没有以可检测的量组装。(d) 在位置264和255处有双突变的菌株显示B带峰值温度下移。它们的B带强度和氧气产量的振荡模式受到高度抑制。这种行为类似于仅在位置264处被修饰的菌株D1和G264。我们扩展了关于突变对除草剂结合影响的加和性的报道，涉及到醌B（QB）的结合。(e) QB位点的突变不仅影响QB和除草剂的结合，还改变了热发光量子产率以及水氧化酶氧化还原态S2和S3的寿命。这一发现可能表明QB位点的结构修饰对光系统II产生了远距离影响。从这些数据我们得出结论，Ser-264对于莠去津、DCMU和QB的结合至关重要，而Phe-255参与莠去津的结合，并且其被Tyr取代不会显著影响集胞藻PCC7942中QB或DCMU的结合。
