Bacteriophage T5 gene D10 encodes a branch-migration protein

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.

Mitochondrial helicase Irc3 translocates along double-stranded DNA

Irc3 is a superfamily II helicase required for mitochondrial DNA stability in Saccharomyces cerevisiae. Irc3 remodels branched DNA structures, including substrates without extensive single-stranded regions. Therefore, it is unlikely that Irc3 uses the conventional single-stranded DNA translocase mechanism utilized by most helicases. Here, we demonstrate that Irc3 disrupts partially triple-stranded DNA structures in an ATP-dependent manner. Our kinetic experiments indicate that the rate of ATP hydrolysis by Irc3 is dependent on the length of the double-stranded DNA cosubstrate. Furthermore, the previously uncharacterized C-terminal region of Irc3 is essential for these two characteristic features and forms a high affinity complex with branched DNA. Together, our experiments demonstrate that Irc3 has double-stranded DNA translocase activity.