Molecular interaction assays between Plasmodium falciparum Sm proteins. (A) Yeast two-hybrid analysis to show interaction between seven P. falciparum Sm proteins. Cotransformants expressing PfSm proteins were selected on the minimal synthetic dropout medium lacking leucine, tryptophan, histidine, and adenine (hereafter termed SD/-Leu-Trp-His-Ade) at 30°C for three to five days. Positive interactions are encircled in red. (B) In vitro interaction studies between seven P. falciparum Sm proteins. In vitro-translated, [35S] -labelled PfSm proteins (PfSmD1, -D2, -D3, -B, -E, -F, -G) were incubated with immobilized GST-PfSm proteins (lanes GST-SmD1, -D2, -D3, -B, -E, -F, -G) or, with GST alone (lane GST) as control. After washing, bound proteins were eluted and analysed by SDS-PAGE and fluorography. Input represents aliquots of radioactive proteins corresponding to 25% of that used in each of the binding reactions. (C) Proposed model of the Plasmodium Sm core complex. The specific heteromeric interactions between the Plasmodium Sm proteins are schematically depicted. Strong (−) and weak (−−) interactions among Sm proteins were indicated using black arrows. Homodimeric interactions are depicted with filled circles.