Promoter choice for expressing HBV surface antigen (HBsAg) In recombinant vaccine development, which promoter has been widely used for cloning and high-level expression of the hepatitis B virus (HBV) surface antigen in yeast-based systems?

Introduction / Context:
Recombinant hepatitis B vaccines are produced by expressing HBsAg in host cells to form immunogenic virus-like particles. Yeast (Saccharomyces cerevisiae) emerged as a safe and scalable production system. The choice of promoter in the expression vector determines transcription strength and, consequently, antigen yield for vaccine manufacture.

Given Data / Assumptions:

• HBsAg is expressed heterologously to assemble into particles resembling viral envelopes.
• Yeast promoters such as ADH1 and GAL1 are common for strong expression.
• Baculovirus polyhedrin promoter is powerful in insect cells, not yeast.

Concept / Approach:

Among the listed promoters, the alcohol dehydrogenase 1 (ADH1) promoter is a strong, constitutive yeast promoter historically used to drive HBsAg expression for licensed recombinant vaccines. While other systems (e.g., baculovirus with polyhedrin promoter) can express HBsAg in insect cells, the question focuses on cloning for vaccine production widely associated with yeast, making ADH1 the most appropriate answer here.

Step-by-Step Solution:

Verification / Alternative check:

Documentation from recombinant vaccine development describes HBsAg expression under yeast promoters (including ADH1), yielding particulate antigen used in commercial vaccines, corroborating promoter choice.

Why Other Options Are Wrong:

Lac promoter is bacterial; polyhedrin is for insect cells; T7 promoter requires T7 polymerase (bacterial systems); galactokinase promoter is not the standard for high-level HBsAg vaccine production.

Common Pitfalls:

Assuming the strongest promoter overall (polyhedrin) is correct without considering host compatibility; promoter choice must match the expression system.

Final Answer:

Alcohol dehydrogenase 1 (ADH1) promoter