The baculovirus single-stranded DNA binding protein, LEF-3, forms a homotrimer in solution

LEF-3 is one of six proteins from Autographa californica multinucleocapsid polyhedrosis virus required for transient DNA replication and has the properties of a single-stranded DNA binding protein. In this report we demonstrate that LEF-3 interacts with itself in both yeast two-hybrid assays and glutathione S-transferase fusion affinity assays. LEF-3 deletion clones which were unable to interact with full-length LEF-3 also failed to support transient DNA replication, suggesting that this interaction is required for the proper function of LEF-3. LEF-3 was purified to homogeneity and characterized by analytical ultracentrifugation and native polyacrylamide gel electrophoresis. These studies revealed that LEF-3 was present as a 132-kDa complex, indicating that its native conformation is that of a homotrimer. This result was confirmed by cross-linking with glutaraldehyde followed by matrix-assisted laser desorption/ionization mass spectrometry.