A RepA-like protein from bacteriophage BFK20 is a multifunctional protein with primase, polymerase, NTPase and helicase activities

The helicase core accessory regions of the phage BFK20 DnaB-like helicase gp43 significantly affect its activity, oligomeric state and DNA binding properties

The multifunctional phage replication protein gp43 is composed of an N-terminal prim-pol domain and a C-terminal domain similar to the SF4-type replicative helicases. We prepared four mutants all missing the prim-pol domain with the helicase core flanked by accessory N- and C-terminal regions truncated to varying extents. The shortest fragment still possessing strong ssDNA-dependent ATPase activity and helicase activity was gp43HEL519-983. The other proteins tested were gp43HEL557-983, gp43HEL519-855 and gp43HEL519-896. Removal of the 38 N-terminal residues in gp43HEL557-983, or the 128 and 87 C-terminal residues in gp43HEL519-855 and gp43HEL519-896, resulted in a significant decrease in the ATPase activities. The 38-amino acid N-terminal region has probably a function in modulating DNA binding and protein oligomerization. Deletion of the 87 C-terminal residues resulted in a twofold increase in the unwinding rate. This region is likely indispensable for binding to DNA substrates.

Gp41, a superfamily SF2 helicase from bacteriophage BFK20

Gp41 is one of two helicases encoded by the genome of bacteriophage BFK20. The gp41 sequence contains conserved motifs from the SF2 family of helicases. We prepared and studied three recombinant proteins: gp41HN, a wild type-like protein with an N-terminal His-Tag; gp41HC, with an S2A mutation and a C-terminal His-Tag; and gp41dC, a mutant protein with a deleted C-terminal region and His-Tags on both N- and C-termini. We tested the enzymatic activities and DNA binding abilities of these isolated proteins. We found that both gp41HN and gp41HC had strong DNA-dependent ATPase activities, but that the ATPase activity of gp41dC was significantly lower regardless of the presence of DNA. The preferred substrates for the NTP hydrolysis reactions were ATP and dATP. gp41HC and gp41HN exhibited a low helicase activity in a fluorescence-based assay using dsDNA substrates with a 3' overhang and with a forked end in the presence of ATP. We infer that the C-terminal region of gp41 may be involved in DNA binding, since removing this region in gp41dC reduced the protein's DNA binding ability.