Which mechanism allows retroviruses to convert RNA into DNA?

Retroviruses possess a unique enzyme called reverse transcriptase, which is crucial for their replication process. This enzyme facilitates the conversion of their RNA genome into DNA, a step that is essential for the virus to integrate into the host's genome and produce new viral particles.

Reverse transcriptase works by first synthesizing a complementary DNA (cDNA) strand based on the RNA template. It then degrades the RNA strand, allowing for the synthesis of a second DNA strand, resulting in a double-stranded DNA molecule. This newly formed DNA can then be integrated into the host cell's DNA by integrase, another viral enzyme. This integration is key for the virus to hijack the host's cellular machinery for its own replication.

The other options listed do not have the capability to perform this specific function. For example, DNA polymerase is involved in DNA synthesis but does not catalyze the conversion of RNA to DNA. RNA replicase is used by some RNA viruses to replicate their RNA but does not convert RNA to DNA. Ligase enzymes are involved in joining DNA fragments but do not perform transcription or reverse transcription. Therefore, reverse transcriptase is the fundamental enzyme that allows retroviruses to reverse-transcribe their RNA into DNA.