How are retroviruses synthesized?

Retroviruses are synthesized primarily by the action of the reverse transcriptase enzyme, which plays a crucial role in their replication cycle. Once a retrovirus enters a host cell, its RNA genome is reverse transcribed into DNA by this enzyme. This process converts the viral RNA into complementary DNA (cDNA), which can then integrate into the host cell's genome. The integrated viral DNA can subsequently be transcribed and translated using the host’s cellular machinery to produce new viral proteins and RNA genomes, ultimately leading to the assembly of new viral particles.

This mechanism distinguishes retroviruses from other viruses, as they utilize reverse transcription, a unique step not found in many other viral replication processes. In the context of the other options, while ribosomes are indeed necessary for translating mRNA into proteins, they are not the primary synthesizing machinery for retroviruses themselves. DNA polymerase is typically involved in DNA replication and does not play a direct role in the synthesis of retroviral genomes from RNA. RNA splicing, which modifies RNA after synthesis, does not apply directly to the synthesis of retroviruses either, as this process is more related to the processing of pre-mRNA in eukaryotic cells rather than the replication of retroviral RNA.