Poliovirus, discovered in 1909 by Landsteiner & Popper, is possibly the best known of all viruses. During the first half of this century poliovirus caused devastating epidemics of poliomyelitis, particularly in countries with improved standards of hygiene. This epidemiological paradox bewildered health officials and caused widespread fear (290, 322) not unlike AIDS does today. As a result, enormous effort was expended in isolating the virus and elucidating its biology.

Poliomyelitis ceased to be a serious health problem in developed countries after the development and successful application of the inactivated (Salk) and live (Sabin) poliovirus vaccines in the 1950s and 1960s. Thereafter, scientific interest in poliovirus waned temporarily until the discovery that genome structure, gene organization, and aspects of replication of poliovirus are unique. As the prototype virus of Picomaviridae, a large family of human and animal viral pathogens, poliovirus is again an intensely studied agent, not least because of the stability of its capsid and the ease with which it can be propagated and purified to near chemical homogeneity. Poliovirus is a strikingly simple self-replicating (living?) entity, consisting of 60 copies each of capsid proteins VP1, VP2, VP3, and VP4, and one copy of a single-stranded RNA genome. Schwerdt & Schaffer reported in 1955 (342) that the poliovirus genome is RNA. The virus was crystallized in 1955 (339), and its three-dimensional structure was solved in 1985 (131). Through sequence analyses of viral RNA (181, 311) and virus-encoded