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?
Correct Answer: YIp
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:
List vector classes and their replication features.Identify that YIp lacks ARS.Conclude YIp integrates and does not replicate autonomously.Select YIp as the correct answer.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