Beclin-1 is a key autophagy protein. Which combination correctly identifies its encoding gene and the autophagy step it primarily participates in?

• A. Encoded by LC3; autophagosome formation
• B. Encoded by BECN1; nucleation
• C. Encoded by ATG5; fusion with lysosome
• D. Encoded by PIK3C3; elongation

Answer: (B)

The function tested is identifying Beclin-1’s encoding gene and its role in autophagy initiation, specifically nucleation. Beclin-1 is encoded by the BECN1 gene. It acts as a key part of the class III PI3K complex that initiates autophagy by generating PI3P at the site of phagophore formation, thereby promoting nucleation of the isolation membrane. This makes Beclin-1 essential for the early step that sets up the autophagosomal membrane.

In contrast, other proteins are associated with different steps: LC3 is linked to the elongation and expansion of the autophagosome; ATG5 participates in the ubiquitin-like conjugation system that drives elongation; PIK3C3 encodes the catalytic subunit of the class III PI3K itself (VPS34), which provides the PI3P but is not the Beclin-1 gene. Therefore, the correct pairing is Beclin-1 encoded by BECN1 and primarily involved in nucleation.