Nakahara D H, Lingappa V R, Chuck S L
Department of Physiology, University of California, San Francisco 94143-0444.
J Biol Chem. 1994 Mar 11;269(10):7617-22.
Signal, stop transfer, and signal-anchor sequences direct a nascent polypeptide to a single topology with respect to the membrane of the endoplasmic reticulum. However, other types of sequences direct nascent proteins, either transiently or permanently, to more than one topologic form. Pause transfer sequences direct nascent apolipoprotein B to pause during its translocation, resulting in nonintegrated, transmembrane intermediates that become fully translocated over time. The stop transfer effector sequence (STE) directs the nascent prion protein either to integrate at the hydrophobic domain which immediately follows (TM1) or to become fully translocated, in a manner dependent on cytosolic factors. Although the action of pause transfer sequences has been dissected into stop and restart steps, the mechanism of STE action is unknown. Using chimeric proteins expressed in vitro, we show that STE, independent of TM1, acts as a pause transfer sequence. We also demonstrate that translocational pausing at STE is a common step preceding either complete translocation or integration into the membrane of a chimeric protein containing STE and TM1. These findings have implications for the role of pausing in the biogenesis of both secretory and membrane proteins.
信号序列、停止转移序列和信号锚定序列可引导新生多肽在内质网膜上形成单一的拓扑结构。然而，其他类型的序列可引导新生蛋白质暂时或永久地形成多种拓扑形式。暂停转移序列可引导新生载脂蛋白B在转运过程中暂停，产生未整合的跨膜中间体，这些中间体随时间推移会完全转运。停止转移效应序列（STE）可引导新生朊病毒蛋白根据胞质因子的作用，要么整合到紧随其后的疏水结构域（TM1），要么完全转运。虽然暂停转移序列的作用已被分解为停止和重新启动步骤，但STE的作用机制尚不清楚。通过体外表达的嵌合蛋白，我们发现STE独立于TM1发挥作用，充当暂停转移序列。我们还证明，在STE处的转运暂停是包含STE和TM1的嵌合蛋白完全转运或整合到膜之前的常见步骤。这些发现对暂停在分泌蛋白和膜蛋白生物发生中的作用具有启示意义。
