Final answer:
In retroviruses, LTRs are restored on the newly made RNA sequence through reverse transcription. The viral RNA is used as a template for the synthesis of complementary DNA strands by reverse transcriptase. The cDNA strands are then integrated into the host genome, forming a provirus.
Step-by-step explanation:
In some RNA viruses, the viral RNA sequence is used directly as mRNA for translation into viral proteins.
However, in retroviruses, which are a type of RNA virus, LTRs (Long Terminal Repeats) are restored on the newly made RNA sequence through a process called reverse transcription.
During reverse transcription, the viral RNA serves as a template for the synthesis of complementary DNA (cDNA) strands by the enzyme reverse transcriptase.
The cDNA strands are then integrated into the host genome, forming a provirus.
The LTRs, which are specific sequences found at both ends of the retroviral genome, play a crucial role in the integration and transcription of the proviral DNA.