A researcher investigates affinity maturation of B cells within germinal centers. Which enzyme is primarily responsible for introducing somatic hypermutation into the variable regions of immunoglobulin genes?
- A RAG1/RAG2 recombinase
- B Activation-induced cytidine deaminase (AID) ✓
- C Terminal deoxynucleotidyl transferase (TdT)
- D DNA-dependent protein kinase (DNA-PK)
Correct answer: B. Activation-induced cytidine deaminase (AID)
Explanation
Activation-induced cytidine deaminase (AID) deaminates cytosine to uracil in single-stranded DNA of immunoglobulin variable regions, initiating somatic hypermutation and class-switch recombination during germinal center reactions. RAG1/RAG2 mediates V(D)J recombination during primary B-cell development, not affinity maturation. TdT adds non-templated nucleotides at V-D-J junctions. DNA-PK repairs double-strand breaks during class switching.
Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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