Uip4, a novel endoplasmic reticulum protein, maintains nuclear shape and cellular homeostasis in S. cerevisiae

Nuclear pore complex (NPC) regulates the transport of macromolecules across the nuclear envelope (NE). In yeast, the NPC is composed of about 30 different proteins, the nucleoporins (Nups). However, the regulation of expression and distribution of the Nups along the NE is largely unknown. In a fluorescence microscopy based genetic screen, we found that presence of Ulp1-interacting proteins (UIPs), is important for NE shape and NPC distribution. We show that the expression status of Uip4p determines quality of NPC structure and function in yeast. Preventing cellular degradation pathways such as macro-autophagy and Endoplasmic Reticulum associated protein degradation (ERAD) suppresses the defects in NPC function caused by either loss or over-expression of Uip4. We show that Uip4 is important for regulating the function and stability of the inner ring component, Nup157p. Our studies identify Uip4 as a novel regulator of NPC homeostasis in yeast.