Terminology — what are the direct repeats flanking Agrobacterium T-DNA called? In Agrobacterium tumefaciens Ti plasmids, the short direct repeats that flank the T-DNA and define its boundaries are known as:

Introduction / Context:Precise terminology matters in genetic engineering. The short, conserved sequences that delimit T-DNA and are recognized by Vir proteins have a specific name used throughout the Agrobacterium literature.

Given Data / Assumptions:

• Direct repeats flank T-DNA and serve as processing sites.
• Recognition by VirD2/VirC occurs at these elements.
• Terminology distinguishes them from unrelated sequence tags in other systems.

Concept / Approach:

These repeats are called border sequences (left border, LB; right border, RB). ‘‘cos’’ refers to lambda phage cohesive ends; ‘‘att’’ refers to phage integration sites; ‘‘flanking sequences’’ is too generic to be precise in this context.

Step-by-Step Solution:

Verification / Alternative check:

Vector maps and Ti plasmid schematics label LB and RB as ‘‘border’’ sequences, confirming standard usage.

Why Other Options Are Wrong:

‘‘cos’’ and ‘‘att’’ belong to bacteriophage biology; ‘‘transfer sequences’’ lacks specificity; ‘‘flanking sequences’’ is non-technical here.

Common Pitfalls:

Using generic or phage-derived terms when the plant transformation field uses ‘‘border’’ precisely.

Final Answer:

Border sequences