title: SARS coronavirus nsp1 protein induces template-dependent endonucleolytic cleavage of mRNAs: viral mRNAs are resistant to nsp1-induced RNA cleavage.
abstract: SARS coronavirus (SCoV) nonstructural protein (nsp) 1, a potent inhibitor of host gene expression, possesses a unique mode of action: it binds to 40S ribosomes to inactivate their translation functions and induces host mRNA degradation. Our previous study demonstrated that nsp1 induces RNA modification near the 5'-end of a reporter mRNA having a short 5' untranslated region and RNA cleavage in the encephalomyocarditis virus internal ribosome entry site (IRES) region of a dicistronic RNA template, but not in those IRES elements from hepatitis C or cricket paralysis viruses. By using primarily cell-free, in vitro translation systems, the present study revealed that the nsp1 induced endonucleolytic RNA cleavage mainly near the 5' untranslated region of capped mRNA templates. Experiments using dicistronic mRNAs carrying different IRESes showed that nsp1 induced endonucleolytic RNA cleavage within the ribosome loading region of type I and type II picornavirus IRES elements, but not that of classical swine fever virus IRES, which is characterized as a hepatitis C virus-like IRES. The nsp1-induced RNA cleavage of template mRNAs exhibited no apparent preference for a specific nucleotide sequence at the RNA cleavage sites. Remarkably, SCoV mRNAs, which have a 5' cap structure and 3' poly A tail like those of typical host mRNAs, were not susceptible to nsp1-mediated RNA cleavage and importantly, the presence of the 5'-end leader sequence protected the SCoV mRNAs from nsp1-induced endonucleolytic RNA cleavage. The escape of viral mRNAs from nsp1-induced RNA cleavage may be an important strategy by which the virus circumvents the action of nsp1 leading to the efficient accumulation of viral mRNAs and viral proteins during infection.
authors.affiliation: Department of Microbiology and Immunology, The University of Texas Medical Branch, Galveston, Texas, United States of America.
authors.forename: Cheng
authors.initials: C
authors.lastname: Huang
authors.forename: Kumari G
authors.initials: KG
authors.lastname: Lokugamage
authors.forename: Janet M
authors.initials: JM
authors.lastname: Rozovics
authors.forename: Krishna
authors.initials: K
authors.lastname: Narayanan
authors.forename: Bert L
authors.initials: BL
authors.lastname: Semler
authors.forename: Shinji
authors.initials: S
authors.lastname: Makino
mesh_terms: D015967:Gene Expression Regulation, Viral / Q000235:genetics*; D020871:RNA Stability; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism*; D012367:RNA, Viral / Q000235:genetics / Q000378:metabolism*; D012324:RNA-Dependent RNA Polymerase / Q000235:genetics / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D045473:Severe acute respiratory syndrome-related coronavirus / Q000235:genetics / Q000378:metabolism*; D013698:Templates, Genetic; D017361:Viral Nonstructural Proteins / Q000235:genetics / Q000378:metabolism*
chemical_list: D012333:RNA, Messenger; D012367:RNA, Viral; D017361:Viral Nonstructural Proteins; C521592:Nsp1 protein, SARS coronavirus; D012324:RNA-Dependent RNA Polymerase