Final answer:
The enzyme responsible for cleaving the interstrand hairpin in V(D)J coding regions is Artemis, which is crucial for the joining of coding segments in the development of immune system diversity.
Step-by-step explanation:
The enzyme that cleaves the interstrand hairpin in V(D)J coding regions during the immune system's development of diversity in B and T cells is Artemis. After the RAG-1/2 complex initiates the recombination process by creating DNA double-strand breaks, Artemis is involved in opening the hairpins that are created at the coding ends. This step is essential for the subsequent joining of coding segments to form the variable regions of antibodies and T-cell receptors.