Final answer:
The conversion of retroviral RNA into linear DNA occurs in the cytoplasm, mediated by the enzyme reverse transcriptase released by the retrovirus upon infection of a host cell.
Step-by-step explanation:
Conversion of retroviral RNA template into the linear DNA occurs in the cytoplasm. The process begins when a retrovirus, such as HIV, infects a host cell. The viral RNA and enzyme reverse transcriptase contained within the virus are released into the cytoplasm. Here, reverse transcriptase catalyzes the synthesis of DNA from the viral RNA template, creating a DNA strand which can then enter the nucleus to integrate with the host's genome.
The initial conversion from RNA to DNA is not performed in the nucleus, nucleolus, or virion matrix, but instead, it happens before the viral contents reach the nucleus. Once the DNA is created, it moves into the nucleus where it can be integrated and replicated. Therefore, the correct answer is 3. Cytoplasm. This process is crucial for the virus to reproduce and is a target for antiretroviral drugs, such as reverse transcriptase inhibitors.