Davis N G, Horecka J L, Sprague G F
Institute of Molecular Biology, University of Oregon, Eugene 97403.
J Cell Biol. 1993 Jul;122(1):53-65. doi: 10.1083/jcb.122.1.53.
The Saccharomyces cerevisiae a-factor receptor (STE3) is subject to two modes of endocytosis: a constitutive process that occurs in the absence of ligand and a regulated process that is triggered by binding of ligand. Both processes result in delivery of the receptor to the vacuole for degradation. Receptor mutants deleted for part of the COOH-terminal cytoplasmic domain are disabled for constitutive, but not ligand-dependent internalization. Trans-acting mutants that impair constitutive endocytosis have been isolated. One of these, ren1-1, is blocked at a late step in the endocytic pathway, as receptor accumulates in a prevacuolar endosome-like compartment. REN1 is identical to VPS2, a gene required for delivery of newly synthesized vacuolar enzymes to the vacuole. Based on this identity, we suggest a model in which the transport pathways to the vacuole--the endocytic pathway and the vacuolar biogenesis pathway--merge at an intermediate endocytic compartment. As receptor also accumulates at the surface of ren1 cells, receptor may recycle from the putative endosome to the surface, or REN1 may also be required to carry out an early step in endocytosis.
酿酒酵母α因子受体（STE3）存在两种内吞作用模式：一种是在没有配体时发生的组成型过程，另一种是由配体结合触发的调节型过程。这两种过程都会导致受体被输送到液泡中进行降解。缺失部分COOH末端细胞质结构域的受体突变体在组成型内吞作用中功能丧失，但在配体依赖性内化过程中功能正常。已分离出损害组成型内吞作用的反式作用突变体。其中之一，ren1-1，在内吞途径的后期步骤被阻断，因为受体积聚在类前液泡内体区室中。REN1与VPS2相同，VPS2是将新合成的液泡酶输送到液泡所必需的基因。基于这种一致性，我们提出了一个模型，其中通向液泡的运输途径——内吞途径和液泡生物发生途径——在中间内吞区室合并。由于受体也在ren1细胞表面积聚，受体可能从假定的内体循环到表面，或者REN1也可能是内吞作用早期步骤所必需的。
