THE EVOLUTION OF MORBILLIVIRUSES - A COMPARISON OF NUCLEOCAPSID GENE-SEQUENCES INCLUDING A PORPOISE MORBILLIVIRUS

Sequence data for the nucleocapsid protein (N) gene of the porpoise mo rbillivirus including the very conserved middle section of the protein and the hypervariable C terminus are reported. Analysis of dissimilar ity indices based on an alignment of the N proteins of various morbill iviruses identifies a variable region of the N protein from amino acid s residues 121 to 145 and a hypervariable part from amino acids 400 to 517. This type of analysis can be usefully applied when protein seque nces of five or more morbillivirus species are available. Regions of v ariability between species identified by this index also represent reg ions of variation within one species e.g. measles virus (MV). Hence, c omparative analysis of different morbilliviruses provides an insight i nto the potentially variable parts of viral proteins. From the great a nd unexplained nucleotide sequence conservation observed within MV, it would appear that the various morbilliviruses have diverged from each other a very long time ago. However, the data do not yet allow us to estimate the time span of these divergences. The relatedness and the n umber of different morbillivirus species provides a unique database fo r study of the evolution of RNA viruses.