Retroviral genomes — What is the genetic material of retroviruses such as HIV within virions?

Introduction:Viruses vary in their genomic composition. Retroviruses are a distinctive class that package one type of nucleic acid in virions yet replicate via a different intracellular intermediate. This question asks for the genome type present inside the viral particle of HIV and related retroviruses.

Given Data / Assumptions:

• Focus is on the packaged genome inside virions, not the intracellular intermediate.
• Retroviruses carry reverse transcriptase.
• Integration into host DNA occurs after infection.

Concept / Approach:Retroviruses package positive-sense single-stranded RNA (two copies per virion). Upon entry, reverse transcriptase synthesizes a double-stranded DNA copy that integrates as a provirus. Thus, the virion genome is RNA, even though a DNA intermediate is essential in the life cycle.

Step-by-Step Solution:

Verification / Alternative check:Biochemical purification of retroviral particles reveals genomic RNA and reverse transcriptase activity; antiretroviral drugs target reverse transcriptase to block conversion of RNA to DNA.

Why Other Options Are Wrong:

• DNA: present only after reverse transcription inside the host cell.
• Protein: structural components exist, but not the genetic material.
• All of these / DNA–RNA hybrid: not accurate descriptions of the packaged genome.

Common Pitfalls:Conflating the packaged genome (RNA) with the replication intermediate (DNA). Retroviruses are defined by RNA genomes plus reverse transcription.

Final Answer:RNA.