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Sheath

Written by the Fiveable Content Team • Last updated August 2025
Written by the Fiveable Content Team • Last updated August 2025

Definition

A sheath is a protective protein layer surrounding the nucleic acid of some viruses. It often plays a role in the injection of the viral genome into host cells.

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5 Must Know Facts For Your Next Test

  1. Sheaths are primarily found in bacteriophages, which are viruses that infect bacteria.
  2. The sheath contracts during infection to inject the viral DNA or RNA into the host cell.
  3. It is composed of proteins that can undergo conformational changes to facilitate genome delivery.
  4. Sheaths are essential for the infectivity of certain viruses, particularly those with complex structures like T4 bacteriophage.
  5. The mechanism of sheath contraction is often compared to a syringe or needle-like action.
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