FUNCTIONAL INTERACTIONS OF GENE-32, GENE-41, AND GENE-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 activ ity. The 59 protein has been recently purified and found to have a spe cific affinity for both 32 protein (single-stranded DNA-binding protei n) and 41 protein (Yonesaki 1994, J. Biol. Chem. 269, 1284-1289). We e xamined the effects of 59 protein on ssDNA-dependent ATPase activity a nd DNA helicase activity of 41 protein in the presence or absence of 3 2 protein. The ATPase activity of 41 protein was strongly inhibited by 32 protein over a wide range of amounts from subsaturation to oversat uration of ssDNA. The 32 protein was also inhibitory toward DNA helica se activity. Addition of 59 protein effectively eliminated these inhib itory effects of 32 protein. Moreover, 59 protein facilitated 41 prote in to overcome the barrier to initiate the unwinding reaction with a d uplex nanking a single-stranded DNA gap. Intriguingly, 32 protein at a n 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 su bstrate molecule containing 2900 nucleotides of ssDNA were required. T hese results strongly suggest that 59 protein modulates 41 protein act ivities by forming a complex with 41 protein and that 41 protein can p roduce recombinogenic ssDNA with the aid of 32 and 59 proteins.