Proteasome assembly utilizes multiple dedicated assembly chaperones and is regulated by signaling pathways that respond to diverse stress conditions. To discover new factors influencing proteasome base assembly, we screened a tiled high-copy yeast genomic library to identify dosage suppressors of a temperature-sensitive proteasome regulatory particle (RP) base mutant. The screen identified Nst1, a protein that when overexpressed, specifically suppressed the temperature sensitivity and proteasome-assembly defects of multiple base mutants. Nst1 overexpression reduced cytosolic RP ATPase (Rpt) aggregates in nas6Δ rpn14Δ cells, which lack two RP assembly chaperones. Nst1 is highly polar and predicted to have numerous intrinsically disordered regions, characteristics commonly found in proteins that can segregate into membraneless condensates. In agreement with this, both endogenous and overexpressed Nst1 could form cytosolic puncta that co-localized with processing body (P-body) components. Consistent with the accumulation of translationally inactive mRNAs in P-bodies, Nst1 overexpression inhibited global protein translation in nas6Δ rpn14Δ cells. Translational inhibition is known to suppress aggregation and proteasome assembly defects in base mutants under heat stress. Our data indicate that Nst1 is a previously overlooked P-body component that when expressed at elevated levels inhibits translation, prevents Rpt subunit aggregation, and rescues proteasome assembly under stress conditions.

蛋白酶体组装利用多个专用的组装伴侣，并由响应不同压力条件的信号通路调节。为了发现影响蛋白酶体碱基组装的新因素，我们筛选了一个平铺的高拷贝酵母基因组文库，以确定温度敏感蛋白酶体调节颗粒 (RP) 碱基突变体的剂量抑制因子。筛选鉴定出 Nst1，一种在过度表达时可特异性抑制多个碱基突变体的温度敏感性和蛋白酶体组装缺陷的蛋白质。Nst1 过表达减少nas6 Δ rpn14中的细胞溶质 RP ATPase (Rpt) 聚集体Δ 细胞，缺乏两个 RP 组装伴侣。Nst1 是高度极性的，并且预计具有许多本质上无序的区域，这些特征通常存在于可以分离成无膜凝聚物的蛋白质中。与此一致，内源性和过表达的 Nst1 都可以形成与加工体（P-体）成分共定位的胞质泪点。与 P 体中翻译失活的 mRNA 的积累一致，Nst1 过表达抑制nas6 Δ rpn14 Δ 细胞中的全局蛋白质翻译。已知翻译抑制可抑制热应激下碱基突变体的聚集和蛋白酶体组装缺陷。我们的数据表明，Nst1 是一种以前被忽视的 P 体成分，当它以升高的水平表达时会抑制翻译，防止 Rpt 亚基聚集，并在压力条件下拯救蛋白酶体组装。