Coronaviruses SD and SK share extensive nucleotide homology with murine coronavirus MHV-A59, more than that shared between human and murine coronaviruses.

A cDNA probe representing the genome of mouse hepatitis virus (MHV) strain A59 (MHV-A59) was used to measure nucleotide sequence homologies among murine and human coronaviruses and the SD and SK coronaviruses isolated by Burks et al. Since SD and SK were isolated by inoculation of multiple sclerosis (MS) central nervous system (CNS) tissue into mice or cultured mouse cells, it is important to determine their relationships to other murine and human coronavirus isolates. Our results indicate that SD and SK share almost complete nucleotide homology (approximately 90%) with MHV-A59 and generate subgenomic RNAs of the same sizes as MHV-A59. The human coronavirus (HCV) strains tested show less homology with MHV-A59. The immunologically unrelated HCV-229E shows no nucleotide homology with MHV-A59. The immunologically cross-reactive HCV-OC43 shows nucleotide homology with MHV-A59 by blot hybridization but not when hybridized in solution and assayed by S1 nuclease digestion.