Competitive Fitness in Coronaviruses Is Not Correlated with Size or Number of Double-Membrane Vesicles under Reduced-Temperature Growth Conditions

Al-Mulla, Hawaa M. N.; Turrell, Lauren; Smith, Nicola M.; Payne, Luke; Baliji, Surendranath; Züst, Roland; Thiel, Volker; Baker, Susan C.; Siddell, Stuart G.; Neuman, Benjamin W.

Some replicase subunits work together in units known as cistrons. Five cistrons (0, I, II, IV, and VI) have been defined, with gaps left in the naming scheme in case new cistrons are discovered that map to nsp13 and nsp15, respectively (14, 23) . Complementation studies using temperature-sensitive (ts) mutants of mouse hepatitis virus (MHV) have showed that mutations in nsp3, nsp12, nsp14, and nsp16 protein define distinct cistrons (cistrons 0, II, IV, and VI, respectively), while mutations in nsp5 and nsp10 proteins define a single cistron (cistron I) (14, (23) (24) (25) . Temperature-sensitive mutations in coronavirus nsp3, nsp5, nsp10, nsp12, nsp14, and nsp16 have been reported, all of which permit RNA synthesis at 33°C but cause RNA synthesis defects at 40°C (14, (24) (25) (26) (27) (28) .