ANALYSIS OF THE INITIAL EVENTS IN THE IN VIVO REPLICATION OF POLIOVIRUS RNA

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Attenuation of neurovirulence in poliovirus appears to be the results of a finite number of nucleotide changes in the viral genome that cause a decrease in the replicative efficiency of the virus. Despite this, the attenuation phenotype can be pleiotropic and difficult to analyze. Differences in replicative efficiency, especially for picornaviruses, should be most pronounced during the initial stages of viral infection when the infecting viral genome initiates the events that lead to the subversion of the cell. We have demonstrated that the low level of poliovirus replication during the expression of the infecting viral genome can be monitored by following the appearance of viral RNA complementary to virion RNA (cRNA). Cellular amplification of virion RNA requires cRNA, which is found neither in virions nor in uninfected cells. Extremely low levels of cRNA have been detected and quantitated using radioactive probes for cRNA and RNA purified from cells early in the infectious cycle. These studies have been extended and simplified through the use of the polymerase chain reaction (PCR), which is being used to delineate the progression of the viral RNA through the initial stages of viral infection.