Cellular Characterization of SARS Coronavirus Nucleocapsid

The Severe and Acute Respiratory Syndrome coronavirus (SARS CoV) is a newlyemerged virus that caused an outbreak of atypical pneumonia in the winter of 2002-2003. Polyclonal antibodies raised against the nucleocapsid (N) of the SARS CoV showed the localization of N to the cytoplasm and the nucleolus in virus-infected and N-expressing Vero E6 cells. Like other coronavirus N proteins, the SARS N is probably a phosphoprotein. N protein expressed in mammalian cells is apparently able to “spread” to neighboring cells. For N to spread to neighboring cells, it must be exported out of the expressing cells. This is shown by the immunoprecipitation of N from the culture medium of a stable cell line expressing myc-N. Deletion studies showed that the 27 kD C-terminal domain of N (C1/2) is the minimal region of N that can spread to other cells. The nucleolar localization and spreading of N are artefacts of fixation, reminiscent of other protein-transduction domain (PTD)-containing proteins.