phi 6 is a lipid-containing dsRNA bacteriophage of Pseudomonas syringae. Its nucleocapsid (NC) has common features with Reoviridae core particles. We report here the crosslinking of phi 6 NC proteins with cleavable 12-A span chemical crosslinker, dithiobis(succinimidyl propionate). The crosslinked complexes were analyzed in two-dimensional polyacrylamide gels or by using monoclonal antibodies to uncleaved protein complexes in one-dimensional protein gels. The NC surface protein (P8) forms a series of multimeric homopolymers. The phi 6 lytic enzyme, protein P5, is associated with P8 on the NC surface. The interior NC proteins P1 and P4, associated with the virus polymerase activity, are also in contact with the P8 shell. A P1 + P4 complex is also formed. Only one of the NC proteins (P7) did not easily form complexes with the other NC proteins. These results indicate a very closely packed P8 surface lattice with specific contacts to the internal NC proteins.