Kjaerulff S, Andersen B, Nielsen V S, Møller B L, Okkels J S
Department of Plant Biology, Royal Veterinary and Agricultural University, Copenhagen, Denmark.
J Biol Chem. 1993 Sep 5;268(25):18912-6.
Photosystem I of barley contains a polypeptide with an apparent molecular mass of 7 kDa when isolated using the detergent n-decyl-beta-D-maltopyranoside. The 7-kDa polypeptide is lost from the PS I complex isolated using Triton X-100. The 7-kDa polypeptide and a corresponding full-length cDNA clone have been isolated. Based on high sequence similarity to an N-terminal sequence of PSI-K from spinach and to the deduced amino acid sequence of Psak from Chlamydomonas reinhardtii the 7-kDa barley polypeptide is identified as PSI-K. The cDNA clone encodes a precursor polypeptide of 131 amino acid residues with a calculated molecular mass of 13,726 Da. The transit peptide shows characteristics of polypeptides imported into the chloroplast. PSI-K has two hydrophobic regions predicted to be membrane-spanning alpha-helices. In vitro expressed prePSI-K polypeptide was imported into intact chloroplasts, whereas an in vitro expressed prePSI-K lacking 7 amino acid residues (Met-Ala-Ser-Gln-Leu-Ser-Ala) at the N-terminal end of the transit peptide failed to be imported. The mRNA encoding PSI-K increases during illumination. PsaK is located in a single locus in the genome. PSI-K has significant similarity to PSI-G. When comparing the barley PSI-K and PSI-G with the reported PSI-K sequence from Synechococcus vulcanus, the degree of similarity is equal, suggesting that an ancestral gene has been duplicated in a chloroplast progenitor but not in a cyanobacterial.
当使用去污剂正癸基-β-D-麦芽糖苷分离时，大麦的光系统I含有一种表观分子量为7 kDa的多肽。使用Triton X-100分离的PS I复合物中会丢失7 kDa的多肽。现已分离出7 kDa的多肽及其相应的全长cDNA克隆。基于与菠菜PSI-K的N端序列以及莱茵衣藻Psak推导的氨基酸序列的高度序列相似性，将7 kDa的大麦多肽鉴定为PSI-K。该cDNA克隆编码一个由131个氨基酸残基组成的前体多肽，计算分子量为13726 Da。转运肽显示出导入叶绿体的多肽的特征。PSI-K有两个预测为跨膜α螺旋的疏水区域。体外表达的prePSI-K多肽可导入完整的叶绿体，而在转运肽N端缺少7个氨基酸残基（Met-Ala-Ser-Gln-Leu-Ser-Ala）的体外表达的prePSI-K则无法导入。编码PSI-K的mRNA在光照期间增加。PsaK位于基因组中的一个单一基因座上。PSI-K与PSI-G有显著相似性。将大麦的PSI-K和PSI-G与已报道的火山集胞藻的PSI-K序列进行比较时，相似程度相同，这表明一个祖先基因在叶绿体祖细胞中发生了复制，但在蓝细菌中没有。
