Final answer:
The enzyme responsible for introducing single-strand breaks between the V(D)J coding sequence and the heptamer RSS is RAG-1/2. These proteins initiate the process of V(D)J recombination, which is crucial for the diversity of the immune system's antigen receptors. Other proteins mentioned are involved in various roles in DNA repair and recombination.
Step-by-step explanation:
The enzyme that introduces single-strand breaks between V(D)J coding sequence and heptamer recombination signal sequences (RSS) is RAG-1/2. RAG-1/2 stands for recombination-activating genes 1 and 2. These proteins form a complex that initiates V(D)J recombination, a crucial process in the development of variability in lymphocyte antigen receptors. V(D)J recombination is an essential mechanism for the generation of diverse antibody repertoires in B cells and diverse T-cell receptor repertoires in T cells.
The entire process involves the recognition of the RSS by RAG-1/2, which then introduces a single-strand break at the border of the coding segment and the RSS. Following the introduction of these breaks, other proteins and enzymes, such as DNA ligases and Ku70/80, are involved in the processing and joining of the DNA ends to form a functional gene segment encoding the antigen receptors.
It is important to note that other options provided in the question have different roles in the processes related to DNA repair and recombination. For instance, Artemis functions alongside RAG in the processing of hairpin-coded ends during V(D)J recombination, XRCC4 with DNA ligase IV is involved in the joining phase, repairing double-strand breaks, and Ku70 and Ku80 are proteins that bind to DNA ends and are part of the non-homologous end joining (NHEJ) repair pathway.