Paradoxes of the replication of picornaviral genomes

A wealth of experimental data on the mechanism of the picornavirus genome r eplication has accumulated. Not infrequently, however, conclusions derived from these data appear to contradict each other. On the one hand, initiatio n of a complementary RNA strand can be demonstrated to occur in a solution containing only the poliovirus RNA polymerase, VPg, uridine triphosphate, p oly(A) template and appropriate ions. On the other hand, convincing experim ents suggest that efficient initiation of a viral complementary RNA strand requires complex cis-acting signals on the viral RNA template, additional v iral and possibly cellular proteins as well as a membrane-containing enviro nment. On the one hand, there is evidence that the viral RNA, in order to b e replicated, should first be translated, but on the other hand, the viral RNA polymerase appears to be unable to overcome the ribosome barrier. Possi ble solutions for these and several other similar paradoxes are discussed, along with less contradictory results on the properties of the picornaviral replicative proteins. Recent results suggesting that recombination and oth er rearrangements of the viral RNA genomes may be accomplished not only by the replicative template switching but also by nonreplicative mechanisms ar e also briefly reviewed. (C) 1999 Elsevier Science B.V. All rights reserved .