Sulli C, Schwartzbach S D
School of Biological Sciences, University of Nebraska, Lincoln 68588, USA.
Plant Cell. 1996 Jan;8(1):43-53. doi: 10.1105/tpc.8.1.43.
The Euglena precursor to the small subunit of ribulose-15-bisphosphate carboxylase/oxygenase (pSSU) is a polyprotein. To determine the transport route from cytoplasm to chloroplast, Euglena was pulse labeled with 35S-sulfate and the organelles were separated on sucrose gradients. After a pulse, pSSU was found in the endoplasmic reticulum (ER) and Golgi apparatus. During a chase, ER-and Golgi-localized pSSU decreased concomitant with the appearance of SSU in chloroplasts. SSU was not found in pSSU-containing ER and Golgi fractions. Na2CO3 did not remove pSSU from ER or Golgi membranes, indicating that it was an integral membrane protein. pSSU was inserted in vitro into canine microsomes, and Na2CO3 did not remove pSSU from the microsomal membrane. The in vivo and in vitro experiments show that Euglena pSSU is inserted into the ER membrane and transported as an integral membrane protein to the Golgi apparatus before chloroplast import and polyprotein processing.
1,5 - 二磷酸核酮糖羧化酶/加氧酶小亚基(pSSU)的眼虫前体是一种多蛋白。为了确定从细胞质到叶绿体的运输途径,用眼虫进行了35S - 硫酸盐脉冲标记,并在蔗糖梯度上分离细胞器。脉冲后,在内质网(ER)和高尔基体中发现了pSSU。追踪过程中发现,ER和高尔基体定位的pSSU减少,同时叶绿体中出现了SSU。在含有pSSU的ER和高尔基体组分中未发现SSU。Na2CO3不能从ER或高尔基体膜上去除pSSU,表示它是一种整合膜蛋白。pSSU在体外插入犬微粒体中时,Na2CO3也不能从微粒体膜上去除pSSU。体内和体外实验表明,眼虫pSSU插入ER膜并作为整合膜蛋白转运到高尔基体,之后再进行叶绿体导入和多蛋白加工。