A cell infected with rabies virus releases a virion with a genome containing a mutation that prevents the matrix (M) protein from being synthesised correctly. What would you expect to occur if this virion infects another cell? The virus will:[Fill in the blank]

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BlackTom AI · Accepted Answer

First, consider what the question is asking: what happens when a rabies virion with a mutation that prevents synthesis of the M (matrix) protein infects a new cell. The Matrix protein in many enveloped negative-sense RNA viruses is typically involved in virion assembly and budding; without functional M, genome replication and viral protein production may still occur, but assembly and release are impaired. Now evaluate each option in turn.

Option a: "be able to enter the host cell, synthesise viral mRNA, but no genome replication will occur." This suggests that entry and transcription can happen, but replication cannot. However, for many negative-sense RNA viruses, transcription of viral mRNA depends on the input genome and replication involves synthesis of antigenomic RNA followed by genome replication. The absence of M would not directly block genome replication at the polymerase level; M mainly affects assembly and release, not necessarily the ability to replicate the genome once replication has started. Therefore saying genome replication cannot occur is not consistent with the typical role of M being linked to assembly.

Option b: "be able to enter the host cell, but no viral mRNA or genome replication will occur." If M is absent, the polymerase complex could still function to transcribe mRNA and replicate the genome in the cytoplasm; entry is not blocked by M deficiency. Thus this option incorrectly asserts a block in transcription and replication solely due to M absence.

Option c: "be able to enter the host cell, synthesise viral mRNA and proteins, and replicate its genome, but assembly or release of new particles will not occur." This aligns with the idea that M is primarily required for assembly and budding. Without functional M, the virus can still transcribe mRNA, translate viral proteins, and replicate its genome, but virions cannot properly assemble and bud from the cell, so new particles are not released. This matches the typical consequence of an M defect in enveloped viruses where replication steps up to genome synthesis proceed, but assembly/release fail.

Option d: "not be able to enter the host cell." The mutation is specific to M synthesis, which does not inherently block receptor binding or entry steps. Therefore entry could still occur, making this option unlikely given the scenario.

In summary, Option a wrongly implies a failure of genome replication due to M loss, Option b wrongly states there would be no transcription or replication, Option d wrongly asserts entry is blocked, while Option c correctly describes that entry, transcription, and replication can occur but assembly/release would be impaired due to the M protein defect. Each incorrect option reveals a misunderstanding about the distinct stages of the viral life cycle—entry, transcription/replication, and assembly/release—clarifying why those stages would or would not depend on the matrix protein.

A cell infected with rabies virus releases a virion with a genome containing a mutation that prevents the matrix (M) protein from being synthesised correctly. What would you expect to occur if this virion infects another cell? The virus will:[Fill in the blank]

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