biostudies-literatureWang LNIGMS NIH HHSeabm8435https://www.ebi.ac.uk/biostudies/studies/S-EPMC8956257biostudies-literatureUnknown8(12)Phosphorylation can quickly switch on/off protein functions. Here, we reported pre-mRNA processing 4 kinase A (PRP4KA), and its paralogs interact with Serrate (SE), a key factor in RNA processing. PRP4KA phosphorylates at least five residues of SE in vitro and in vivo. Hypophosphorylated, but not hyperphosphorylated, SE variants could readily rescue <i>se</i> phenotypes in vivo. Moreover, hypophosphorylated SE variants had stronger binding affinity to microprocessor component HYL1 and were more resistant to degradation by 20<i>S</i> proteasome than hyperphosphorylated counterparts. Knockdown of the kinases enhanced the accumulation of hypophosphorylated SE. However, the excessive SE interfered with the assembly and function of SE-scaffolded macromolecule complexes, causing the <i>se</i>-liScience advancesPRP4KA phosphorylates SERRATE for degradation via 20<i>S</i> proteasome to fine-tune miRNA production in <i>Arabidopsis</i>.PMC8956257R01 GM132401Shang BChoi SWLi YZhang XChhajed SChen SYan XWang ZWang LZhao HfalsePRP4KA phosphorylates SERRATE for degradation via 20<i>S</i> proteasome to fine-tune miRNA production in <i>Arabidopsis</i>.Phosphorylation can quickly switch on/off protein functions. Here, we reported pre-mRNA processing 4 kinase A (PRP4KA), and its paralogs interact with Serrate (SE), a key factor in RNA processing. PRP4KA phosphorylates at least five residues of SE in vitro and in vivo. Hypophosphorylated, but not hyperphosphorylated, SE variants could readily rescue <i>se</i> phenotypes in vivo. Moreover, hypophosphorylated SE variants had stronger binding affinity to microprocessor component HYL1 and were more resistant to degradation by 20<i>S</i> proteasome than hyperphosphorylated counterparts. Knockdown of the kinases enhanced the accumulation of hypophosphorylated SE. However, the excessive SE interfered with the assembly and function of SE-scaffolded macromolecule complexes, causing the <i>se</i>-li2022-01-01T00:00:00Z2022 Mar2026-06-18T08:50:31.92Z2025-04-19T20:12:41.027ZS-EPMC89562573533356610.1126/sciadv.abm8435