"was found to be phosphorylated in a cell cycle-specific manner; it was found phosphorylated in interphase but not in mitotic cells"

"During interphase, however, two forms of p115 were detected in the cells; the phosphorylated form was found exclusively in cytosol, whereas the unphosphorylated form was associated with membranes, mostly of the Golgi complex."

"Mutational analysis revealed that the phosphorylation site of p115 was the Ser942 residue in the C-terminal acidic domain."

"A mutant with a single substitution of Ser942 --> Ala markedly increased its association with the Golgi membrane."

"Another mutant with Ser942 --> Asp was able to associate with the membrane, although at a decreased level"

"these results suggest that the phosphorylation of Ser942 at the C-terminal acidic domain regulates the interaction of p115 with the Golgi membrane"

"Human **USO1/p115** is a conserved **ERGIC/cis-Golgi vesicle tether/fusion factor** in early secretory trafficking, connecting Rab1-regulated vesicle capture/docking with SNARE-dependent membrane fusion."

"p115/USO1 is described as a **Golgi vesicle tethering protein** that promotes **vesicle docking and fusion**, in part through binding to SNARE machinery and Rab GTPase–dependent recruitment."

"A widely used framework is that **Rab1 (RAB1A/B)** on COPII vesicles recruits p115/USO1 at the ER–Golgi interface, and p115 then helps organize or stabilize **cis-Golgi SNARE complex assembly**, promoting membrane fusion. A 2023 thesis synthesis explicitly states that p115 has been shown to interact with **Rab1A via its N-terminus** and that p115 interacts with cis-Golgi SNAREs (e.g., Sec22b, Bet1, GOSR2, syntaxin-5) in proposed fusion models."

"A 2023 thesis synthesis states that **GM130 binds p115 at its N-terminus** and that this interaction can be blocked by **Cdk1 phosphorylation of GM130 S37** during mitosis, consistent with mitotic reorganization of the Golgi."

"A human-cell study reports that the p115 head domain can bind directly to Sec16A, with mutations that disrupt motif binding reducing secretion efficiency, providing a mechanistic link between a Golgi tether and ER exit-site scaffolding."

"Human p115/USO1 localizes to the **ERGIC and cis-Golgi**, cycling on/off membranes and acting at early secretory trafficking steps. A human-cell study describes p115 as anchored to Golgi membranes, acting at the ER–Golgi interface, and adds functional coupling to ER exit sites via binding to Sec16A."

"A 2023 eLife study (fungal Uso1; homolog of human p115) reports that the **globular head domain directly binds SNAREs** (including Bet1 and Bos1/membrin family members) and that a **monomeric head domain** can complement loss of full-length Uso1 in vivo when overexpressed—arguing that long-range coiled-coil tethering can be dispensable and that the essential role can involve **direct regulation of SNARE machinery**."

"yeast/fungal Uso1/p115 head domains adopt an **armadillo-repeat/alpha-solenoid** organization, and the protein includes long coiled-coils implicated in tethering-distance/geometry. Human-centric sources in this set largely describe p115 as a **dimer with an N-terminal head and coiled-coil tail**."

"a 2022 Science Advances study shows that the Legionella effector **LegA15** hijacks host **p115**, inducing host **Golgi fragmentation** and altering lipid-droplet homeostasis. Proteomics identified p115/USO1 as a top putative interactor with high peptide support"

"in human HCC, a tumor-associated isoform **USO1-T** correlates with poorer prognosis, promotes aggressive behavior, causes **Golgi unstacking**, and accelerates trafficking from ER to Golgi/plasma membrane; modeling suggests weakened dimerization/GM130 tethering and involvement of **ERK** and **GRASP65**."

"A 2024 phosphoproteomics/proteomics study of **treatment-naive RA synovial biopsies (n=8)** reports that **USO1 Ser48** was the phosphosite with the **highest inverse correlation with ESR** in their analysis, illustrating that USO1 is phosphorylated in human inflammatory tissue and that specific phosphosites can correlate with clinical measures."