Construction of yeast episomal plasmids (YEp) YEp cloning vectors were historically engineered from which key components?

Introduction / Context:
Yeast episomal plasmids (YEp) are shuttle vectors that replicate in both Escherichia coli and Saccharomyces cerevisiae. Their design allows convenient DNA manipulation in bacteria and functional expression or selection in yeast.

Given Data / Assumptions:

• 2μm plasmid is a natural, high-copy yeast plasmid providing replication functions in S. cerevisiae.
• pBR322 provides bacterial origin of replication and antibiotic resistance for propagation in E. coli.
• Inclusion of yeast nuclear DNA fragments can supply selectable markers (for example, LEU2, URA3).

Concept / Approach:

By combining the 2μm sequences (for yeast replication), yeast marker genes (for selection), and a bacterial backbone (for cloning and amplification), YEp vectors function as classic shuttle plasmids. This architecture enables rapid cloning in E. coli and subsequent transformation and high-copy maintenance in yeast.

Step-by-Step Solution:

Verification / Alternative check:

Textbook diagrams of YEp vectors consistently show 2μm-derived sequences, a yeast marker, and pBR322-derived sequences, validating the composition.

Why Other Options Are Wrong:

Options omitting pBR322 (or substituting pMB9) or the 2μm element fail to provide dual-host replication/selection; 12μm plasmid is not a standard yeast replicon; mitochondrial or T7 components are not typical for YEp.

Common Pitfalls:

Confusing YEp with YRp (ARS-based) or YIp (integrative) vectors; YEp specifically leverages 2μm for stable episomal maintenance.

Final Answer:

2μm yeast plasmid, fragments of yeast nuclear DNA, and E. coli vector pBR322