Poliovirus lacks a 5' cap but is still translated. Which mechanism explains how translation initiates in this virus?

Poliovirus lacks a 5' cap but is still translated. Which mechanism explains how translation initiates in this virus?

• A. Cap-dependent initiation
• B. Ribosome shunting
• C. Internal ribosome entry site
• D. It uses transcriptional control elements in the 3' UTR

Answer: (C)

Poliovirus initiates translation without a 5' cap by using an internal ribosome entry site in its 5' untranslated region. This IRES directly recruits the ribosome to an internal site near the start codon, enabling cap-independent translation of the viral polyprotein. In infected cells, the virus also impairs cap-dependent translation by cleaving host initiation factors, reinforcing reliance on the IRES. Cap-dependent initiation requires a 5' cap and eIF4F, which the virus lacks in its genome. Ribosome shunting is a different mechanism not used by poliovirus, and 3' UTR transcriptional control elements don’t drive translation initiation in this RNA virus.

Poliovirus initiates translation without a 5' cap by using an internal ribosome entry site in its 5' untranslated region. This IRES directly recruits the ribosome to an internal site near the start codon, enabling cap-independent translation of the viral polyprotein. In infected cells, the virus also impairs cap-dependent translation by cleaving host initiation factors, reinforcing reliance on the IRES. Cap-dependent initiation requires a 5' cap and eIF4F, which the virus lacks in its genome. Ribosome shunting is a different mechanism not used by poliovirus, and 3' UTR transcriptional control elements don’t drive translation initiation in this RNA virus.