Fig. 6. In vitro binding of the bacterially expressed N-terminal domain of Drosophila LBR (amino acids 17-262 of the dLBR) and Xenopus LBR (amino acids 4-210 of the XLBR) to sperm chromatin. Soluble proteins of heat-treated Xenopus egg extract (S₂₀₀) supplemented with dLBR (A) or XLBR (B) were incubated in the presence (+Sp) (lanes 2, 4) or absence (–Sp) (lanes 1, 3) of demembranated sperm chromatin, then fractionated into supernatants (S) and pellets (P) by centrifugation. Proteins of each fraction and of sperm chromatin that had not been incubated (SP; lane 5) were separated by SDS-PAGE and analyzed by immunoblotting with antibodies against the dLBR (A) and XLBR (B). The distinct polypeptide bands (A, lane 4) labeled by the dLBR antibodies in the relative molecular weight range M_r 60,000 to M_r 200,000 represent oligomeric complexes of the dLBR that had been formed at the sperm chromatin during incubation. The XLBR also forms some oligomeric complexes in the presence of sperm chromatin. Arrows (A,B) mark non-aggregated LBR. Molecular masses of reference proteins (in kDa) are marked.