THE BACULOVIRUS SINGLE-STRANDED-DNA BINDING-PROTEIN, LEF-3, FORMS A HOMOTRIMER IN SOLUTION

LEF-3 is one of six proteins from Autographa californica multinucleoca psid polyhedrosis virus required for transient DNA replication and has the properties of a single-stranded DNA binding protein. In this repo rt we demonstrate that LEF-3 interacts,vith itself in both yeast two-h ybrid 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 th is interaction is required for the proper function of LEF-3, LEF-3 was purified to homogeneity and characterized by analytical ultracentrifu gation and native polyacrylamide gel electrophoresis, These studies re vealed that LEF-3 was present as a 132-kDa complex, indicating that it s native conformation is that of a homotrimer. This result was confirm ed by cross-linking with glutaraldehyde followed by matrix-assisted la ser desorption/ionization mass spectrometry.