Sequences of the nucleocapsid genes from two strains of avian infectious bronchitis virus.

cDNAs prepared from viral genomic RNA purified from two strains of infectious bronchitis virus (IBV) (Beaudette and M41) have been cloned into pBR322. Three of these clones, which contain the complete sequences of mRNA A for both strains, except for the leader sequences which are only present on the subgenomic messenger RNAs, have been sequenced using the dideoxy method. The sequences are similar for both strains, each containing a single long open reading frame of 1227 bases which predicts a polypeptide of molecular weight approximately 45 000. The genome position and size of this predicted polypeptide are consistent with it being the gene for the nucleocapsid protein. The amino acid sequence shows considerable homology with those of the nucleocapsids of murine hepatitis virus strains A59 and JHM. The major difference between the sequences determined for the two IBV strains is that the 3' non-coding region of the Beaudette strain contains a 184 base segment which is not present in the M41 strain.