Baculovirus biology — role of polyhedrin protein In baculoviruses, what is the functional significance of the polyhedrin protein?

Introduction / Context:
Baculoviruses are widely used as expression vectors in insect cells. Understanding the roles of structural proteins is crucial for vector design. Polyhedrin is a hallmark protein forming occlusion bodies in infected insect larvae and plays a special role distinct from genome replication.

Given Data / Assumptions:

• Two phenotypic forms: budded virus for cell-to-cell spread, and occlusion-derived virus protected by polyhedrin matrix for environmental persistence.
• Cell culture expression systems often delete polyhedrin to insert foreign genes.

Concept / Approach:
Polyhedrin forms crystalline occlusion bodies (polyhedra) that encase virions, protecting them in the environment and facilitating oral infection in insect hosts. However, polyhedrin is not required for virus replication in cultured cells, enabling replacement of the polyhedrin locus with heterologous genes under strong promoters for high-level expression.

Step-by-Step Solution:

Verification / Alternative check:
Commercial baculovirus systems (e.g., using AcMNPV) routinely leverage the polyhedrin locus; viable replication in Sf9/Sf21 cells without polyhedrin is well documented.

Why Other Options Are Wrong:

• Absolutely essential for replication: contradicted by polyhedrin-minus vectors.
• DNA polymerase subunit: polyhedrin is a structural protein, not a replication enzyme.

Common Pitfalls:
Assuming all abundant viral proteins are replication enzymes; here abundance serves environmental stability and transmission in larvae.

Final Answer:
Both (a) and (b)