Fleischmann MM, Rochaix JD
Departments of Molecular Biology and Plant Biology, University of Geneva, 1211 Geneva 4, Switzerland.
Plant Physiol. 1999 Apr;119(4):1557-66. doi: 10.1104/pp.119.4.1557.
We have changed the potential phosphorylation site, a threonine residue at position 2 of the D2 polypeptide of the photosystem II complex of Chlamydomonas reinhardtii, to alanine, valine, aspartate, proline, glycine, or glutamate. Mutants with neutral amino acid changes did not display any phenotype with regard to photoautotrophic growth, light sensitivity, fluorescence transients, or photoinhibition. Pulse labeling of these mutants with 32P indicated that a phosphorylated protein of the same size as D2 is absent in these mutants, suggesting that threonine-2 is indeed the unique phosphorylation site of D2. In contrast, mutants in which threonine-2 has been replaced with acidic residues are deficient in photosystem II. Use of chimeric genes containing the psbD 5'-untranslated region revealed that the initiation of translation was not affected in these mutants, but the mutations interfered with a later step of D2 synthesis and accumulation.
我们已将莱茵衣藻光系统II复合物D2多肽第2位的苏氨酸残基这一潜在磷酸化位点替换为丙氨酸、缬氨酸、天冬氨酸、脯氨酸、甘氨酸或谷氨酸。中性氨基酸改变的突变体在光合自养生长、光敏感性、荧光瞬变或光抑制方面未表现出任何表型。用32P对这些突变体进行脉冲标记表明，这些突变体中不存在与D2大小相同的磷酸化蛋白，这表明苏氨酸-2确实是D2的唯一磷酸化位点。相反，苏氨酸-2被酸性残基取代的突变体在光系统II方面存在缺陷。使用含有psbD 5'-非翻译区的嵌合基因表明，这些突变体中翻译起始未受影响，但这些突变干扰了D2合成和积累的后期步骤。
