Johnson E S, Schwienhorst I, Dohmen R J, Blobel G
Laboratory of Cell Biology, Howard Hughes Medical Institute, Rockefeller University, New York, NY 10021, USA.
EMBO J. 1997 Sep 15;16(18):5509-19. doi: 10.1093/emboj/16.18.5509.
SMT3 is an essential Saccharomyces cerevisiae gene encoding a 11.5 kDa protein similar to the mammalian ubiquitin-like protein SUMO-1. We have found that Smt3p, like SUMO-1 and ubiquitin, can be attached to other proteins post-translationally and have characterized the processes leading to the activation of the Smt3p C-terminus for conjugation. First, the SMT3 translation product is cleaved endoproteolytically to expose Gly98, the mature C-terminus. The presence of Gly98 is critical for Smt3p's abilities to be conjugated to protein substrates and to complement the lethality of a smt3Delta strain. Smt3p undergoes ATP-dependent activation by a novel heterodimeric enzyme consisting of Uba2p, a previously identified 71 kDa protein similar to the C-terminus of ubiquitin-activating enzymes (E1s), and Aos1p (activation of Smt3p), a 40 kDa protein similar to the N-terminus of E1s. Experiments with conditional uba2 mutants showed that Uba2p is required for Smt3p conjugation in vivo. Furthermore, UBA2 and AOS1 are both essential genes, providing additional evidence that they act in a distinct pathway whose role in cell viability is to conjugate Smt3p to other proteins.
SMT3是酿酒酵母中的一个必需基因，编码一种11.5 kDa的蛋白质，该蛋白质与哺乳动物泛素样蛋白SUMO-1相似。我们发现，Smt3p与SUMO-1和泛素一样，可以在翻译后与其他蛋白质结合，并对导致Smt3p C末端激活以进行缀合的过程进行了表征。首先，SMT3翻译产物经内切蛋白酶切割以暴露成熟的C末端Gly98。Gly98的存在对于Smt3p与蛋白质底物缀合以及补充smt3Delta菌株的致死性的能力至关重要。Smt3p通过一种新型异二聚体酶进行ATP依赖性激活，该酶由Uba2p（一种先前鉴定的71 kDa蛋白质，类似于泛素激活酶（E1s）的C末端）和Aos1p（Smt3p激活）（一种40 kDa蛋白质，类似于E1s的N末端）组成。对条件性uba2突变体的实验表明，Uba2p在体内是Smt3p缀合所必需的。此外，UBA2和AOS1都是必需基因，这提供了额外的证据，表明它们在一条独特的途径中起作用，其在细胞活力中的作用是将Smt3p与其他蛋白质缀合。
