Technical Abstract: Purification of SINV-1 from its host, Solenopsis invicta, and subsequent examination by electron microscopy revealed a homogeneous fraction of spherical particles with a diameter of 30-35 nm. Quantitative PCR with SINV-1-specific oligonucleotide primers verified that this fraction contained high copy numbers of the SINV-1 genome. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the SINV-1 purified fraction revealed 3 major and 1 minor protein bands. The protein bands were labeled VP1 (40.8 ±1.4 kDa), VP2 (35.7 ±2.8 kDa), VP3 (25.2 ±1.8 kDa), and VP4 (22.2 ±2.5 kDa) based on mass. N-terminal sequence was acquired successfully for VP1, VP2, and VP3, but not VP4, and delineated each capsid protein within the 3'-proximal open reading frame. Positional organization of the viral proteins within the SINV-1 structural polyprotein were consistent with other dicistroviruses (when based on homology). Blastp analysis of SINV-1 VP1, VP2, and VP3 revealed significant homology with corresponding structural capsid proteins of positive-strand RNA viruses. The most significant homologues with the highest identities to the SINV-1 VPs included Acute bee paralysis virus (ABPV), Kashmir bee virus (KBV) and Israeli acute paralysis virus (IAPV). Phylogenetic analyses of the viral proteins confirmed the close relationship between SINV-1, ABPV, IAPV, and KBV in that these viruses formed a distinct clade among insect-infecting dicistroviruses. Amino acid residues about the scissile bonds for VP1 and VP3 were consistent with other dicistroviruses and insect-infecting picorna-like viruses.