THE GENE 59 PROTEIN OF BACTERIOPHAGE-T4 MODULATES THE INTRINSIC AND SINGLE-STRANDED DNA-STIMULATED ATPASE ACTIVITIES OF GENE-41 PROTEIN, THE T4-REPLICATIVE DNA HELICASE

The T4 gene 59 protein (gp59) serves as an accessory protein to the es sential T4-encoded DNA helicase, the gene 41 protein (gp41). gp59 stim ulates gp41-dependent DNA synthesis reactions by promoting the assembl y of gp41 onto single-stranded DNA (ssDNA), where the enzyme is activa ted to perform its DNA helicase functions. To better understand the me chanism of helicase-ssDNA assembly, we have studied the effects of gp5 9 on the intrinsic and ssDNA-stimulated ATPase activities of gp41. Our results indicate that gp59 exerts a direct effect upon the conformati on and ATPase activity of gp41, by increasing the affinity of gp41 for ATP. In addition, we find that gp59 is nearly essential for promoting the assembly of gp41 onto ssDNA molecules that are covered with satur ating amounts of the T4 encoded helix-destabilizing protein, gene 32 p rotein (gp32). Results of protein affinity chromatography experiments suggest that gp59 contains distinct binding sites for gp41 and gp32 an d may therefore act as a molecular adapter between the helicase and he lix-destabilizing proteins. Together, the data indicate that specific gp59-gp41 and gp59-gp32 protein-protein interactions both play importa nt roles in the assembly of the helicase onto single-stranded DNA.