Current Review: RNA Polymerases of Plus-Strand RNA Viruses of Plants. R. Quadt. Department of Biochemistry, Gorlaeus Laboratories, Leiden University, Leiden, The Netherlands. E. M. J. Jaspars. Department of Biochemistry, Gorlaeus Laboratories, Leiden University, Leiden, The Netherlands.. MPMI 2:219-223. Accepted 2 May 1989. Copyright 1989 The American Phytopathological Society.