Functional interactions of gene 32, 41, and 59 proteins of bacteriophage T4

Genes 41 and 59 of bacteriophage T4 are involved in DNA recombination as well as in DNA replication. The 41 protein has a DNA helicase activity. The 59 protein has been recently purified and found to have a specific affinity for both 32 protein (single-stranded DNA-binding protein) and 41 protein (Yonesaki 1994, J. Biol. Chem. 269, 1284-1289). We examined the effects of 59 protein on ssDNA-dependent ATPase activity and DNA helicase activity of 41 protein in the presence or absence of 32 protein. The ATPase activity of 41 protein was strongly inhibited by 32 protein over a wide range of amounts from subsaturation to oversaturation of ssDNA. The 32 protein was also inhibitory toward DNA helicase activity. Addition of 59 protein effectively eliminated these inhibitory effects of 32 protein. Moreover, 59 protein facilitated 41 protein to overcome the barrier to initiate the unwinding reaction with a duplex flanking a single-stranded DNA gap. Intriguingly, 32 protein at an amount optimal for saturation of ssDNA stimulated the overcoming of the barrier when 59 protein was present. For the best circumvention of this initiation barrier, only eight monomers of 59 protein/one DNA substrate molecule containing 2900 nucleotides of ssDNA were required. These results strongly suggest that 59 protein modulates 41 protein activities by forming a complex with 41 protein and that 41 protein can produce recombinogenic ssDNA with the aid of 32 and 59 proteins.