LAUSR

Dear Editor, The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a novel emerging coronavirus that has spread worldwide since breaking out in late 2019 and has led to hundreds of millions of infections and millions of human deaths (Zhou et al., 2020). The genome of SARS-CoV-2 encodes 29 viral proteins, including four structural proteins: spike (S), envelope (E), membrane (M), and nucleocapsid (N) (Kim et al., 2020). N protein is essential for viral genomic RNA replication and packaging and it also plays an important role in the virus– host interactions (Lang et al., 2021). The amino acid sequences of N protein are highly conserved among coronaviruses (Supplementary Figure S1). Accumulating evidence indicates that N protein is a phosphoprotein and its phosphorylation state is important for its proper function (Peng et al., 2008; Wu et al., 2014). Here, we try to map the phosphorylation sites in N protein of SARS-CoV-2 and investigate their functions. Flag-tagged N protein was expressed in HEK293T cells and the phosphorylation level of N protein was detected by immunoprecipitation followed by western blotting assay. As expected, the phosphorylation can be easily detected by anti-phospho-serine (S)/threonine (T) antibody (Figure 1A), implying that the N protein is highly phosphorylated in cells. Then, a large amount of N protein was immunoprecipitated and analyzed by mass spectrom-