Distinct modes of stress granule assembly mediated by the KH‐type RNA‐binding protein Rnc1

Abstract We have previously identified the KH ‐type RNA ‐binding protein Rnc1 as an important regulator of the posttranscriptional expression of the MAPK phosphatase Pmp1 in fission yeast. Rnc1 localization in response to stress has not been elucidated thus far. Here, we report the dual roles of Rnc1 in assembly of stress granules ( SG s), nonmembranous cytoplasmic foci composed of messenger ribonucleoproteins. Rnc1 can localize to poly(A)‐binding protein (Pabp)‐positive SG s upon various stress stimuli, including heat shock ( HS ) and arsenite treatment. Furthermore, Rnc1 deletion results in decreased SG s, indicating that Rnc1 is a new component and a regulator of SG s. Notably, Rnc1 translocates to the dot‐like structures faster than Pabp, and this stress‐induced Rnc1 translocation does not require its RNA ‐binding ability, as the Rnc1 KH 1,2,3 GD mutant protein with impaired RNA ‐binding activity forms dots rather more efficiently than the wild‐type Rnc1 upon HS . Interestingly, in the absence of stress, Rnc1 overproduction induced massive aggregation of Pabp‐positive SG s and eIF 2α phosphorylation. In clear contrast, overproduction of the Rnc1 KH 1,2,3 GD mutant failed to induce Pabp aggregation and eIF 2α phosphorylation, indicating that Rnc1 overproduction‐induced SG assembly requires Rnc1 RNA ‐binding activity. Collectively, Rnc1 regulates SG assembly, dependently or independently of its RNA ‐binding activity.