Presence of ARS — which yeast vector lacks autonomous replication? Autonomously replicating sequence (ARS) elements enable plasmids to replicate independently in yeast. Which vector class does not carry an ARS and therefore integrates for maintenance?

Introduction / Context:ARS sequences in yeast function as replication origins. Vector classes are distinguished by whether they carry ARS (and other elements) or rely on chromosomal integration.

Given Data / Assumptions:

• YRp: ARS-based replicative plasmids.
• YEp: 2μm-based episomal plasmids (functionally analogous to ARS-driven replication).
• YCp: usually include both CEN and ARS.
• YIp: lack ARS and integrate into chromosomes.

Concept / Approach:

Without an ARS (or 2μm origin), a plasmid cannot persist as a free replicon in yeast. YIp vectors thus use homologous recombination to integrate into chromosomal DNA and are inherited with the genome, providing high stability but low copy number.

Step-by-Step Solution:

Verification / Alternative check:

Vector maps and manuals confirm absence of ARS in YIp, distinguishing them from YRp/YEp/YCp/YAC-based systems.

Why Other Options Are Wrong:

YRp, YEp, YCp, and YAC have replication elements; they do not require integration for maintenance.

Common Pitfalls:

Assuming all yeast plasmids are autonomously replicating; YIp is the exception by design.

Final Answer:

YIp