3CL4:
reference: Structure of coronavirus hemagglutinin-esterase offers insight into corona and influenza virus evolution., Zeng Q, Langereis MA, van Vliet AL, Huizinga EG, de Groot RJ, Proc Natl Acad Sci U S A. 2008 Jul 1;105(26):9065-9. Epub 2008 Jun 11. PMID: 18550812

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