Of the viruses highlighted in Section 33.4, predict which of the following would be able to make viral proteins if nothing more than its genome were injected into a suitable host cell. a. pea mosaic ([+]ssRNA) virus b. bluetongue (dsRNA) virus c. measles ([−]ssRNA) virus d. human immunodeficiency (RNA reverse-transcribing) virus

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1. Identify the type of RNA each virus contains and understand the implications for protein synthesis. Positive-sense single-stranded RNA ([+]ssRNA) can be directly translated into proteins by the host's ribosomes. Double-stranded RNA (dsRNA) and negative-sense single-stranded RNA ([−]ssRNA) require transcription into a positive-sense RNA before translation can occur. RNA reverse-transcribing viruses need to reverse transcribe their RNA into DNA, which then needs to be transcribed into mRNA.
2. Analyze the pea mosaic virus, which has a [+]ssRNA genome. Since [+]ssRNA can act as mRNA, this virus can directly make viral proteins using the host's ribosomes once its genome is injected into the cell.
3. Consider the bluetongue virus with a dsRNA genome. This type of RNA cannot be directly translated into proteins. The virus must first use its own RNA-dependent RNA polymerase to transcribe the dsRNA into positive-sense mRNA, which is not possible if only the genome is injected without the necessary viral enzymes.
4. Evaluate the measles virus, which contains a [−]ssRNA genome. Similar to dsRNA viruses, [−]ssRNA cannot be directly translated into proteins. It requires transcription into a complementary [+]ssRNA by viral RNA-dependent RNA polymerase, which must be present in the virion or in the host cell.
5. Assess the human immunodeficiency virus, an RNA reverse-transcribing virus. This virus must first reverse transcribe its RNA into DNA, which then needs to be integrated into the host's genome and transcribed into mRNA. This process requires viral reverse transcriptase and integrase enzymes, which are not available if only the genome is injected.