Coronavirus nucleocapsid proteins assemble constitutively in high molecular oligomers

Cong, Yingying; Kriegenburg, Franziska; de Haan, Cornelis A. M.; Reggiori, Fulvio

The S45 supernatant was then applied onto the same continuous 5-20% glycerol gradient employed for the analysis of the size of recombinant N protein complexes. Interestingly, cytoplasmic N protein from MHV-infected cells was exclusively detected in the last fractions of the gradient similarly to recombinant N protein, while GAPDH was found only in the low-density fractions ( Fig. 2b and c) . A small difference in size between the MHV N protein oligomers formed in vitro and in vivo, however, was detected. This could be due to either a slight inhibition of recombinant N protein self-interaction caused by the 6xHis tag, or a better oligomerization in vivo because of cellular factors such as molecular chaperones. Moreover, it cannot be excluded that there are host proteins that associate to N protein oligomers.