RNA viruses possess the potential for rapid evolution and serve as excellent models to test evolutionary theory. Molecular phylogenetic analysis of the P gene for a large number of diverse natural isolates of vesicular stomatitis virus reveals no evidence for a molecular clock but instead shows a stepwise evolutionary pattern unlike that ever seen before. Each step out from the tree's ancestral root to terminal branch tips correlates not with time of virus isolation but with a south-to-north geographical progression from Panama to the United States. The grossly unequal rates of change within this single species imply an underlying mechanism at odds with the prevailing notion that neutral changes are the dominating feature of molecular evolution. This is also a demonstration of punctuated equilibrium at the molecular level.The error-prone nature of genetic replication in RNA viruses, together with their short generation times and large population sizes, makes them excellent models to test molecular evolutionary theory. As RNA virus genetic replicative machinery is generally about a millionfold more error prone than that of organismal DNA, detailed analysis of RNA virus evolution over a 50-year period is essentially equivalent to study of an organismal system over a 50-million-year period (1).Vesicular stomatitis virus (VSV), a model RNA virus, has a genome of -11 kb, the complete nucleotide sequence of which has been determined for standard strains of both the New Jersey (NJ) and Indiana (IN) serotypes (2). Like most, if not all, RNA viruses, VSV has the potential for rapid genome evolution, as the viral RNA polymerase synthesizes products with an error frequency of :1-20 x 10-4 (3). The virus can grow in a wide range of tissue culture cells. Infection cycles take less than 24 hr and result in approximately 104-to The publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. §1734 solely to indicate this fact. accumulate significant variation in primary amino acid sequence which is reflected in considerable variability in the nucleotide sequence of the gene region encoding this domain. We report here that the nucleotide sequence of a 450-base fiagment of the genome (including the coding sequence for the hypervariable region) has been determined for 149 diverse VSV NJ isolates. ¶ Detailed phylogenetic analysis of the data set indicated an evolutionary pattern that has not, to our knowledge, been described previously.
MATERIALS AND METHODSVirus Growth and RNA Preparation. Low-passage stocks of 149 VSV NJ isolates spanning a 50-year period and from throughout North and Central America (see Fig. 2) were kindly provided by Bob Tesh, Gene Erickson, John Mason, Luis Roquebert, Fred Schaffer, Bruce Francy, and Tom Walton. Included were the standard strains Ogden (../49UTB) and Hazelhurst (../43MOP). Also provided were seven VSV IN isolates, 09/82HDB, 01/85GMB, ../870AB, ../87VCB, 08/84PNB, 02/84PNH, a...