Final answer:
The primer for reverse transcriptase in retroviruses, such as HIV, is a specific tRNA molecule that is complementary to the viral RNA genome, providing a starting point for DNA synthesis.
Step-by-step explanation:
The enzyme reverse transcriptase is critical in converting viral RNA into DNA for retroviruses like HIV. During this conversion, reverse transcriptase requires a primer to initiate the synthesis of DNA. This primer is a short segment of RNA that is complementary to the viral RNA. In the case of HIV and other retroviruses, the primer for reverse transcriptase is provided by a specific tRNA molecule that is bound to the viral RNA genome. The tRNA serves as a starting point for the reverse transcriptase to synthesize the first DNA strand, which will eventually lead to a double-stranded DNA molecule after further replication processes.