Long terminal repeats (LTRs) are found in retroviral DNA, flanking functional genes. They are used to integrate into host genomes.

Example

For example, a retrovirus genome might contain the following features:

LTR -- PBS -- PSI -- gag -- pol -- env -- LTR

LTR = U3RU5

• LTR - Long terminal repeats
• PBS - Primer binding site
• PSI - packaging site
• gag, pol, env - proteins used in viral infection and reproduction

Transcription

The LTRs are partially transcribed into an RNA intermediate, followed by reverse transcription into complementary DNA (cDNA) and ultimately dsDNA (double-stranded DNA) with full LTRs. The LTRs then mediate integration of the retroviral DNA via an LTR specific integrase into another region of the host chromosome.

Retroviruses such as Human Immunodeficiency Virus (HIV) use this basic mechanism.

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