Clark S E, Lamppa G K
Department of Molecular Genetics and Cell Biology, University of Chicago, 920 E. 58th Street, Chicago, Illinois 60637.
Plant Physiol. 1992 Feb;98(2):595-601. doi: 10.1104/pp.98.2.595.
We have investigated whether the precursors for the light-harvesting chlorophyll a/b binding proteins (LHCP) of photosystems II and I (PSII and PSI) are cleavable substrates in an organelle-free reaction, and have compared the products with those obtained during in vitro import into chloroplasts. Representatives from the tomato (Lycopersicon esculentum) LHCP family were analyzed. The precursor for LHCP type I of PSII (pLHCPII-1), encoded by the tomato gene Cab3C, was cleaved at only one site in the organelle-free assay, but two sites were recognized during import, analogous to our earlier results with a wheat precursor for LHCPII-1. The relative abundance of the two peptides produced was investigated during import of pLHCPII-1 into chloroplasts isolated from plants greened for 2 or 24 hours. In contrast to pLHCPII-1, the precursors for LHCP type II and III of PSI were cleaved in both assays, giving rise to a single peptide. The precursor for LHCP type I of PSI, encoded by gene Cab6A, yielded two peptides of 23.5 and 21.5 kilodaltons during import, whereas in the organelle-free assay only the 23.5 kilodalton peptide was found. N-terminal sequence analysis of this radiolabeled peptide has tentatively identified the site cleaved in the organelle-free assay between met40 and ser41 of the precursor.
我们研究了光系统II和I（PSII和PSI）的捕光叶绿素a/b结合蛋白（LHCP）的前体在无细胞器反应中是否为可切割的底物，并将产物与体外导入叶绿体过程中获得的产物进行了比较。分析了番茄（Lycopersicon esculentum）LHCP家族的代表。由番茄基因Cab3C编码的PSII的I型LHCP前体（pLHCPII-1）在无细胞器检测中仅在一个位点被切割，但在导入过程中识别出两个位点，这与我们早期对小麦LHCPII-1前体的研究结果类似。在将pLHCPII-1导入从绿化2小时或24小时的植物中分离的叶绿体的过程中，研究了产生的两种肽的相对丰度。与pLHCPII-1不同，PSI的II型和III型LHCP前体在两种检测中均被切割，产生单一肽段。由基因Cab6A编码的PSI的I型LHCP前体在导入过程中产生了两条分别为23.5和21.5千道尔顿的肽段，而在无细胞器检测中仅发现了23.5千道尔顿的肽段。对该放射性标记肽段的N端序列分析初步确定了在无细胞器检测中前体的met40和ser41之间被切割的位点。
