Botany Department, University of Georgia, Athens, Georgia 30602.
Plant Physiol. 1983 Jul;72(3):847-54. doi: 10.1104/pp.72.3.847.
The coordinated synthesis of the subunits of ribulose 1,5-bisphosphate carboxylase was examined by analysis of the chloroplast ribosome-deficient mutant of Chlamydomonas reinhardtii, ac20crl. The absence of the chloroplast-synthesized large subunit of this enzyme from cells of this strain is a direct consequence of the lack of chloroplast ribosomes. In contrast, the absence of the cytoplasmically-synthesized small subunit of ribulose 1,5-bisphosphate carboxylase from this mutant is not understood. To discern the cause of this absence, we have compared results of in vivo radioactive labeling experiments with those of cell-free translations of RNA from ac20crl. Protein products from these experiments were identified by one-and two-dimensional electrophoretic analyses. Neither subunit, revealed either as a stained band or by fluorography of proteins radioactively labeled in vivo for 2 hours, was detected in ac20crl. Cell-free translation of polyadenylated RNA obtained from ac20crl, however, revealed wild-type levels of mRNA for the precursor to the small subunit. This messenger was found to be associated with subribosomal RNP and polysomes. We conclude that the absence of the small subunit of ribulose 1,5-bisphosphate carboxylase from ac20crl is the result of a translational or posttranslational event.
我们通过分析衣藻 ac20crl 的叶绿体核糖体缺陷突变体，研究了核酮糖 1,5-二磷酸羧化酶的亚基的协调合成。该酶的叶绿体合成的大亚基从该菌株的细胞中缺失，这是叶绿体核糖体缺乏的直接结果。相比之下，这种突变体中细胞质合成的核酮糖 1,5-二磷酸羧化酶的小亚基缺失则无法理解。为了弄清这种缺失的原因，我们比较了 ac20crl 的体内放射性标记实验结果与无细胞翻译 RNA 的结果。这些实验的蛋白质产物通过一维和二维电泳分析进行鉴定。无论是作为染色带还是通过体内标记的蛋白质放射性自显影，都没有在 ac20crl 中检测到两个亚基。然而，从 ac20crl 获得的多聚腺苷酸化 RNA 的无细胞翻译揭示了小亚基前体的 mRNA 水平与野生型相同。这种信使与亚核糖体 RNP 和多核糖体相关。我们得出结论，ac20crl 中核酮糖 1,5-二磷酸羧化酶的小亚基缺失是翻译或翻译后事件的结果。
