Practice question

RecBCD is 330 kDa tri-subunit complex acting as primary double-strand break processing machine in Escherichia coli. RecB contains N-terminal SF1 helicase and C-terminal nuclease domains, RecD provides second SF1 helicase of opposite polarity with 5'→3' movement, while RecC is catalytically inert recognition subunit with channel for Chi. Both RecB motor drives 3'→5' translocation and RecD drives 5'→3' translocation enabling rapid unwinding up to 1000 base pairs per second. Upon Chi recognition nuclease activity switched, generating 3' tail for RecA loading mediated via RecB domain contacting RecA.