Final answer:
RecBCD is an enzyme complex with Helicase and Nuclease activities essential for the homologous recombination repair of double-stranded DNA breaks.
Step-by-step explanation:
RecBCD is a multifunctional enzyme complex that plays a critical role in the homologous recombination DNA repair pathway, particularly in the repair of double-stranded breaks (DSBs). The different enzymatic activities of RecBCD include Helicase activity, which unwinds the double-stranded DNA at the site of the break, and Nuclease activity, which degrades the unwound DNA ends to create single-stranded DNA overhangs. Moreover, RecBCD has a Chi recognition activity, which upon recognizing a specific DNA sequence known as Chi (crossover hotspot instigator), alters its nuclease activity to produce single-stranded DNA that is conducive to the binding of RecA protein.
The significance of each activity in homologous recombination via the DSB-repair pathway is as follows: The Helicase activity is essential for unwinding the DNA to allow subsequent steps of repair. Nuclease activity is critical for processing the DNA ends to form the single-stranded overhangs necessary for strand invasion during recombination. Finally, the Chi recognition and altered nuclease activity facilitate the formation of stable RecA nucleoprotein filaments, which are pivotal for searching for and aligning with the homologous sequence on the sister chromatid, leading to DNA strand exchange and repair.