*The sequence data have been deposited with the EMBL/GenBank database under
accession no. Y-07568.
Arch Virol (1997) 142: 749—763
Evolutionary relationships in the ilarviruses: nucleotide sequence
of prunus necrotic ringspot virus RNA 3*
J. A. Sa´ nchez-Navarro and V. Palla´s
Departamento de Mejora y Patologia Vegetal, CEBAS (CSIC), Murcia, Spain
Accepted September 25, 1996
Summary. The complete nucleotide sequence of an isolate of prunus necrotic
ringspot virus (PNRSV) RNA 3 has been determined. Elucidation of the amino
acid sequence of the proteins encoded by the two large open reading frames
(ORFs) allowed us to carry out comparative and phylogenetic studies on the
movement (MP) and coat (CP) proteins in the ilarvirus group. Amino acid
sequence comparison of the MP revealed a highly conserved basic sequence
motif with an amphipathic -helical structure preceding the conserved motif of
the ‘30K superfamily’ proposed by Mushegian and Koonin  for MP’s.
Within this ‘30K’ motif a strictly conserved transmembrane domain is present in
all ilarviruses sequenced so far. At the amino-terminal end, prune dwarf virus
(PDV) has an extension not present in other ilarviruses but which is observed in
all bromo- and cucumoviruses, suggesting a common ancestor or a recombina-
tional event in the Bromoviridae family. Examination of the N-terminus of the
CP’s of all ilarviruses revealed a highly basic region, part of which resembles the
Arg-rich motif that has been characterized in the RNA-binding protein family.
This motif has also been found in the other members of the Bromoviridae family,
suggesting its involvement in a structural function. Furthermore this region is
required for infectivity in ilarviruses. The similarities found in this Arg-rich motif
are discussed in terms of this process known as genome activation. Finally,
phylogenetic analysis of both the MP and CP proteins revealed a higher
relationship of A1MV to PNRSV, apple mosaic virus (ApMV) and PDV than
any other member of the ilarvirus group. In that sense, A1MV should be
considered as a true ilarvirus instead of forming a distinct group of viruses.
The prunus necrotic ringspot virus (PNRSV) is the causal agent of several
diseases aﬀecting most cultivated stone fruits, including cherry, sour cherry,