Vitellogenin (Vtg) is a lipid transfer protein that carries yolk to the ovary. The vitellogenin receptor (VtgR) mediates the uptake of Vtg into the oocyte of oviparous animals; its structure includes eight ligand-binding repeats (LBR). The binding site of VtgR and Vtg and the location of the interaction within the molecules are at these LBR. Positively charged Vtg residues are important for binding with acidic clusters in VtgR. This test describes experiments designed to analyze the molecular mechanism involved in protein interaction between VtgR and Vtg and location within the molecules. (Contains 4 figures.)