Barnes Laboratory, Department of Molecular Genetics and Cell Biology, The University of Chicago, Chicago, Illinois 60637.
Plant Physiol. 1986 Jan;80(1):43-51. doi: 10.1104/pp.80.1.43.
The apoprotein of the major light harvesting pigment-protein complex from the diatom Phaeodactylum tricornutum (UTEX 646) is composed of two similar polypeptides of 17.5 and 18.0 kilodaltons (kD). The in vivo synthesis of these polypeptides is inhibited by the 80s protein synthesis inhibitor cycloheximide, but not by the 70s ribosome inhibitor chloramphenicol. When total poly(A)(+) RNA was used in in vitro protein synthesis, a number of polypeptides were synthesized with a dominant product at 22 kD. When the polypeptides were immunoprecipitated with monospecific antibodies to the 17.5 and 18.0 polypeptides, a single protein zone of 22 kD was detected. Immunoprecipitation with preimmune serum failed to precipitate detectable levels of protein at any relative molecular weight (M(r)). These findings indicate that the two apoprotein polypeptides of the diatom light harvesting pigment-protein are translated from polyadenylated message on cytoplasmic ribosomes as either a single or two (or more) similar M(r) precursor proteins. These findings also suggest that this protein is encoded in the nucleus.Photosynthetic light adaptation features of P. tricornutum UTEX 646 indicate that it responds to low light by increasing cell size and numbers of photosystem I and II reaction centers per cell, but does not change photosynthetic rate per cell or photosynthetic unit sizes significantly. When low light cells are exposed to higher photon flux densities, the in vivo incorporation of label into the apoprotein of the light harvesting complex decreases. In contrast, high light grown cells show rapid (<3 hour) increases in apoprotein synthesis when exposed to low light levels. This is the first demonstration of a specific role of photon flux density in regulating the synthesis of a major light harvesting pigment-protein during photosynthetic light adaptation.
甲藻（Phaeodactylum tricornutum UTEX 646）主要光捕获色素蛋白复合物的脱辅基蛋白由两条分子量约为 17.5 和 18.0 千道尔顿（kD）的相似多肽组成。在活体中，80s 蛋白合成抑制剂环己亚胺可以抑制这两条多肽的合成，而 70s 核糖体抑制剂氯霉素则不能。当使用总 poly(A)(+)RNA 进行体外蛋白质合成时，会合成许多多肽，其中一个主要产物的分子量为 22 kD。当用针对 17.5 和 18.0 多肽的单特异性抗体进行免疫沉淀时，只检测到分子量为 22 kD 的单一蛋白区带。用免疫前血清进行免疫沉淀时，在任何相对分子质量（M(r)）下都未能沉淀到可检测水平的蛋白质。这些发现表明，甲藻光捕获色素蛋白的两个脱辅基蛋白是由细胞质核糖体上的多聚腺苷酸化信使翻译而来的，它们可以作为单一或两个（或更多）相似 M(r)的前体蛋白。这些发现还表明，该蛋白是在细胞核中编码的。P. tricornutum UTEX 646 的光合作用光适应特征表明，它通过增加细胞大小和每个细胞中 PSI 和 PSII 反应中心的数量来响应低光，而不会显著改变每个细胞的光合速率或光合单位大小。当低光细胞暴露在更高的光子通量密度下时，光捕获复合物脱辅基蛋白在体内的标记掺入量会减少。相比之下，高光生长的细胞在暴露于低光水平时会迅速（<3 小时）增加脱辅基蛋白的合成。这是首次证明光子通量密度在调节光合作用光适应过程中主要光捕获色素蛋白的合成方面具有特定作用。
