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U1 snRNP proteins promote proximal alternative polyadenylation sites by directly interacting with 3′ end processing core factors
Zhijie Hu1,† , Mengxia Li1,† , Zhanfeng Huo1,† , Liutao Chen1 , Susu Liu1 , Ke Deng1 , Xin Lu1 , Shangwu Chen1 , Yonggui Fu1,* , Anlong Xu1,2,*
1State Key Laboratory of Biocontrol, Guangdong Province Key Laboratory of Pharmaceutical Functional Genes, Department of Biochemistry, School of Life Sciences, Sun Yat-sen University, Higher Education Mega Center, Guangzhou 510006, China
2School of Life Sciences, Beijing University of Chinese Medicine, Beijing 100029, China
These authors contributed equally to this work.
*Correspondence to:Yonggui Fu , Anlong Xu ,
J Mol Cell Biol, Volume 14, Issue 8, August 2022, mjac054,

In eukaryotic cells, both alternative splicing and alternative polyadenylation (APA) play essential roles in the gene regulation network. U1 small ribonucleoprotein particle (U1 snRNP) is a major component of spliceosome, and U1 snRNP complex can suppress proximal APA sites through crosstalking with 3′ end processing factors. However, here we show that both knockdown and overexpression of SNRPA, SNRPC, SNRNP70, and SNRPD2, the U1 snRNP proteins, promote the usage of proximal APA sites at the transcriptome level. SNRNP70 can drive the phase transition of PABPN1 from droplet to aggregate, which may reduce the repressive effects of PABPN1 on the proximal APA sites. Additionally, SNRNP70 can also promote the proximal APA sites by recruiting CPSF6, suggesting that the function of CPSF6 on APA is related with other RNA-binding proteins and cell context-dependent. Consequently, these results reveal that, on the contrary to U1 snRNP complex, the free proteins of U1 snRNP complex can promote proximal APA sites through the interaction with 3′ end processing machinery.