Early phage enzymes: Many RNA bacteriophages synthesize, very early after infection, an RNA-dependent RNA polymerase. What is the standard name for this enzyme?

Introduction / Context: Positive-sense RNA bacteriophages (and many RNA viruses) must copy their RNA genomes using an enzyme that uses RNA as a template to make RNA. In classical texts, the term “RNA replicase” refers to this RNA-dependent RNA polymerase activity encoded by the virus.

Given Data / Assumptions:

• The enzyme template is RNA, and the product is RNA.
• “RNA replicase” is a historic but still widely recognized term for viral RNA-dependent RNA polymerase.
• Only one option names this function precisely.

Concept / Approach: Enzyme names track template and product. DNA-dependent RNA polymerases transcribe DNA to RNA; RNA-dependent RNA polymerases replicate RNA to RNA. For RNA phages, this early enzyme is essential to amplify viral RNA and synthesize minus and plus strands.

Step-by-Step Solution: Identify the template: RNA. Identify the product: RNA. Match to canonical name: RNA replicase (RNA-dependent RNA polymerase). Exclude ligases and reverse transcriptase (RNA → DNA).

Verification / Alternative check: Biochemical purification from RNA phage-infected cells yields a virus-specific polymerase that copies RNA templates, classically termed RNA replicase.

Why Other Options Are Wrong: “RNA polymerase” without qualifier usually implies DNA-dependent; “RNA transcriptase” is nonstandard; “RNA ligase” joins RNA ends; “reverse transcriptase” copies RNA to DNA.

Common Pitfalls: Equating cellular transcription with viral RNA replication; they use different templates and enzymes.

Final Answer: RNA replicase.