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 <em>not</em> 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