<Tr> <Td> RecC </Td> <Td> gamma </Td> <Td> P07648 </Td> <Td> Likely recognizes Chi (crossover hotspot instigator) </Td> </Tr> <Tr> <Td> RecD </Td> <Td> alpha </Td> <Td> P04993 </Td> <Td> 5' - 3' helicase </Td> </Tr> <P> Both the RecD and RecB subunits are helicases, i.e., energy - dependent molecular motors that unwind DNA (or RNA in the case of other proteins). The RecB subunit in addition has a nuclease function . Finally, RecBCD enzyme (perhaps the RecC subunit) recognizes a specific sequence in DNA, 5' - GCTGGTGG - 3', known as Chi (sometimes designated with the Greek letter χ). </P> <P> RecBCD is unusual amongst helicases because it has two helicases that travel with different rates and because it can recognize and be altered by the Chi DNA sequence . RecBCD avidly binds an end of linear double - stranded (ds) DNA . The RecD helicase travels on the strand with a 5' end at which the enzyme initiates unwinding, and RecB on the strand with a 3' end . RecB is slower than RecD, so that a single - stranded (ss) DNA loop accumulates ahead of RecB (Figure 2). This produces DNA structures with two ss tails (a shorter 3' ended tail and a longer 5' ended tail) and one ss loop (on the 3' ended strand) observed by electron microscopy . The ss tails can anneal to produce a second ss loop complementary to the first one; such twin - loop structures were initially referred to as "rabbit ears ." </P>

Which subunits of the recbcd trimer show helicase structure and function