Nakamoto H, Hasegawa M
Department of Biochemistry and Molecular Biology, Saitama University, Urawa, Japan.
Plant Cell Physiol. 1999 Jan;40(1):9-16. doi: 10.1093/oxfordjournals.pcp.a029479.
Mutant strains of the unicellular cyanobacterium Synechocystis sp. PCC 6803, in which the psaK gene was insertionally inactivated by targeted mutagenesis, were constructed. The gene is one of the two potential PsaK-coding genes which have been found as a result of the genome project with this cyanobacterium. One of the mutants was characterized in detail. A monocistronic, 480-nucleotide mRNA of psaK was absent in total RNA from the mutant cells. Inactivation of psaK had little effect on the accumulation of polypeptides in the isolated PSI complexes except for a polypeptide with an apparent molecular mass of 4.6 kDa which was absent in the mutant. The amino-terminal amino acid sequence of the 4.6-kDa polypeptide confirmed that it was the translation product of psaK and further revealed a presequence of PsaK. Characteristics of photoautotrophic growth at different temperatures, the amount of chlorophyll per cell, photosynthetic electron transport rates with rates with various electron acceptors, the kinetics of charge recombination between P700+ and reduced FA/FB, and the molar ratio of chlorophyll to P700, of the mutant were not significantly different from those of the wild type. Furthermore, the trimer to monomer ratio of the PSI complexes isolated from the mutant was similar to that isolated from the wild type.
构建了单细胞蓝藻集胞藻6803（Synechocystis sp. PCC 6803）的突变株，其中psaK基因通过靶向诱变被插入失活。该基因是通过对这种蓝藻进行基因组计划而发现的两个潜在的PsaK编码基因之一。对其中一个突变体进行了详细表征。突变体细胞的总RNA中不存在单顺反子的、480个核苷酸的psaK mRNA。除了突变体中不存在的一种表观分子量为4.6 kDa的多肽外，psaK的失活对分离的PSI复合物中多肽的积累影响很小。4.6 kDa多肽的氨基末端氨基酸序列证实它是psaK的翻译产物，并进一步揭示了PsaK的前导序列。该突变体在不同温度下的光合自养生长特性、每个细胞的叶绿素含量、与各种电子受体的光合电子传递速率、P700 +与还原型FA/FB之间的电荷复合动力学以及叶绿素与P700的摩尔比，与野生型没有显著差异。此外，从突变体中分离的PSI复合物的三聚体与单体比例与从野生型中分离的相似。
