Journal of General Virology (1990), 71, 2791-2799. Printed in Great Britain 2791 Nucleotide sequences of coat protein genes for three isolates of barley yellow dwarf virus and their relationships to other luteovirus coat protein sequences J. R. Vincent,* P. P. Ueng,t R. M. Lister and B. A. Larkins~ Department of Botany and Plant Pathology, Lilly Hall of Life Sciences, Purdue University, West Lafayette, Indiana 47907, U.S.A. Barley yellow dwarf virus (BYDV) can be separated into two groups based on, among other criteria, serological relationships that are presumably governed by the viral capsid structure. Nucleotide sequences for the coding regions of coat proteins of approximately 22 K were identified for the MAV-PS 1, P-PAV (group 1) and NY-RPV (group 2) isolates of BYDV, The MAV-PS1 and P-PAV coat protein sequences shared 71% deduced amino acid similarity whereas that of the NY-RPV isolate shared no more than 51% similarity with either the MAV-PSI or the P-PAV sequence. Other comparisons showed that these and other BYDV coat protein sequences examined to date share a high degree of identity with those identified from other luteoviruses. Among luteovirus coat protein sequences in general, several highly conserved domains were identified whereas other domains differentiate MAV- PSI and PAV isolates from NY-RPV and other luteoviruses. Sequence similarities and differences among BYDV coat proteins (approx, 22K) are consis- tent with the serological relationships exhibited by these viruses. Amino acid sequence comparisons between BYDV isolates that share common aphid vectors indicate that it is unlikely that these coat proteins are involved in aphid specificity. Introduction Luteoviruses cause yellowing diseases on a wide range of host plants (Matthews, 1982). They are transmitted obligately by aphid vectors in a persistent, circulative manner and are limited to the phloem tissue of the host plant. Many luteoviruses exhibit some degree of serologi- cally inter-relatedness (Waterhouse et al., 1988; Rochow & Duffus, 1981), and yet they can be grouped into clusters based on the closeness of the serological relationships. Barley yellow dwarf virus (BYDV), the type member of the luteoviruses (Matthews, 1982), comprises a group of serologically related viruses that infect barley, oats, wheat, rice and other graminaceous hosts (Rochow, 1970a). Isolates of BYDV were originally distinguished by, and named according to, their predominant aphid vectors (Rochow, 1970a). They can also be separated into two major groups based on serological relationships (Aapola & Rochow, 1971; Rochow, 1970a; Rochow & Carmichael, 1979; Rochow & Duffus, 1981), cytopatho- t Present address: USDA-ARS,BARC-West,Building 006, Belts- ville, Maryland 20705, U.S.A. :~ Present address: Department of Plant Science, University of Arizona, Tucson, Arizona 85721, U.S.A. 0000-9689 © 1990SGM logical ultrastructure of infected cells (Gill & Chung, 1979), and the profiles of dsRNAs obtained from infected tissue (Gildow et al., 1983). Group I includes the representative isolates: MAV, transmitted by Macros# phum (= Sitobion) avenae Fabr. ; PAV, transmitted by M. avenae and Rhopalosiphum padi L. ; and SGV, transmit- ted by Schizaphis graminum Rond. (Rochow, 1970a). Group 2 includes the representative isolates: RMV, transmitted by R. maidis Fitch. ; and RPV, transmitted by R. padi (Rochow, 1970a). The differences in both serological and aphid vector relationships among BYDV isolates are presumed to reflect differences in viral coat proteins (Rochow, 1970b). The characterization of coat protein genes from different isolates should therefore provide a more detailed understanding of the serological and vectorial relationships exhibited by these viruses. Coat protein nucleotide sequences have been obtained from several luteoviruses, including potato leafroll virus (PLRV) (Kawchuk et al., 1989; Prill et al., 1989), beet western yellows virus (BWYV) (Veidt et al., 1988) and a PAV- like BYDV isolate from Victoria, Australia (Miller et al., 1988a), herein referred to as Vic-PAV. Furthermore, complete genome nucleotide sequences have been reported for BWYV (Veidt et al., 1988), PLRV (Mayo et