Bovine coronavirus nucleocapsid protein processing and assembly.

The coronavirus nucleocapsid protein (N) encapsidates the genomic RNA to form a helical nucleocapsid. The requirements for coronavirus nucleocapsid assembly are being studied. Two forms (approximately 50 kDa and 55 kDa) of the bovine coronavirus (BCV) N protein were detected in infected cells. However, only one form, a 50 kDa species, was detected in extracellular virions. After treatment with calf intestinal alkaline phosphatase (CIAP), the 55 kDa intracellular form increased in mobility to comigrate with the 50 kDa form; whereas, the 50 kDa intracellular species and N from extracellular virions was not sensitive to CIAP treatment. The data indicate that specificity exists with regard to assembly of N into the mature virion. The data suggests that processing of N may take place during assembly of either nucleocapsids or virions and that the processing may be a dephosphorylation event.