Scott M P, Nielsen V S, Knoetzel J, Andersen R, Møller B L
Department of Plant Biology, Royal Veterinary and Agricultural University, Frederiksberg, Copenhagen, Denmark.
Plant Mol Biol. 1994 Nov;26(4):1223-9. doi: 10.1007/BF00040704.
A full-length cDNA clone encoding the PSI-F subunit of barley photosystem I has been isolated and sequenced. The open reading frame encodes a precursor polypeptide with a deduced molecular mass of 24837 Da. The barley PSI-F precursor contains a bipartite presequence with characteristics similar to the presequences of proteins destined to the thylakoid lumen. In vitro import studies demonstrate that an in vitro synthesized precursor is transported across the chloroplast envelope and directed to the thylakoid membrane, where it accumulates in a protease-resistant form. Incubation of the precursor with a chloroplast stromal extract results in processing to a form intermediate in size between the precursor and mature forms. Hydrophobicity analysis of the barley PSI-F protein reveals a hydrophobic region predicted to be a membrane spanning alpha-helix. The hydrophobic nature of PSI-F combined with a bipartite presequence is unusual. We postulate that the second domain in the bipartite presequence of the PSI-F precursor proteins is required to ensure the proper orientation of PSI-F in the thylakoid membrane. The expression of the PsaF gene is light-induced similar to other barley photosystem I genes.
已分离并测序了一个编码大麦光系统I的PSI-F亚基的全长cDNA克隆。开放阅读框编码一个推导分子量为24837 Da的前体多肽。大麦PSI-F前体包含一个二分前导序列，其特征与定位于类囊体腔的蛋白质的前导序列相似。体外导入研究表明，体外合成的前体可穿过叶绿体包膜并定向到类囊体膜，在那里它以蛋白酶抗性形式积累。将前体与叶绿体基质提取物一起孵育会导致加工成大小介于前体和成熟形式之间的中间形式。对大麦PSI-F蛋白的疏水性分析揭示了一个预计为跨膜α-螺旋的疏水区域。PSI-F的疏水性与二分前导序列相结合是不寻常的。我们推测，PSI-F前体蛋白二分前导序列中的第二个结构域是确保PSI-F在类囊体膜中正确定向所必需的。PsaF基因的表达与其他大麦光系统I基因一样受光诱导。
