The ORF of genome segment 6 (S6) ofrice ragged stunt oryzavirus (RRSV) Philippines isolate was cloned and sequenced based on the S6 sequence of the Thailand isolate. Pns6, the 71 kD product of S6expressed in E. coli, was demonstrated to be a viral non-structural protein of RRSV by Weste blotting.The gel mobility shift assays showed that Pns6 had nucleic acid binding activity. Pns6 could interact with single- and double-stranded forms of DNA and RNA, showing a preference for single-stranded nucleic acid and a slight preference for RRSV ssRNA over the rice ssRNA, as demonstrated by both competition and displacement assays. The binding of Pns6 to nucleic acids is strong and sequence non-specific. By using five truncated derivatives of Pns6, it was found that the basic region from amino acid 201 to 273 of Pns6 was the unique nucleic acid binding domain. Subcellular fractionation of leaf tissues of RRSV-infected rice plants and subsequent Weste blotting had shown that Pns6 accumulated predominately in the cytoplasmic membrane fraction. The possible role of RRSV Phs6 in virus replication and assembly is discussed.