Reverse Transcription

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Slide 1

Reverse Transcription

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Central Dogma

Slide 3

Normal transcription involves synthesis of RNA from DNA.

Reverse transcription is the transcription of single stranded RNA into double stranded DNA

With the help of the enzyme Reverse Transcriptase.

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Reverse Transcriptase also known as RNA directed DNA Polymerase

- DNA Nucleotidyl transferase (RNA directed)

- Revertase

Reverse Transcriptase was discovered by Howard Temin and Baltimore in 1970 independently

- shared Nobel Prize in Physiology or Medicine in 1975 for their discovery.

Slide 5

Reverse transcriptase common in Retrovirus.

- HIV

M-MLV (Moloney Murine Leukemia Virus)

AMV (Avian Myeloblastosis Virus)

Reverse Transcriptase enzyme includes two activity: DNA polymerase and RNase H

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Retrovirus Replication Cycle

ds DNA

Provirus

host DNA

Packaging into virus ; budding

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Antiviral drug

Zidovudine

Lamivudine

Tenfovir

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Typical retrovirus has three or four genes.

Gag-pol- env

Retrovirus are called + strand because viral RNA itself code for protein products.

Reverse transcriptase enzyme code for proteins are called – strand

R : Redundant or repeating seq – 10-80

U5: 80 – 100

U3: 170-1350

Like DNA polymerase, Reverse transcriptase requires primers.

tRNA of the host is Primer

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Mechansim Of Retrovirus Replication

1. A Retrovirus specific cellular tRNA hybridizes with a complementary region called PBS (Primer Binding Sites)

2. Reverse Transcriptase (RT) starts at this binding site and copies RNA into a single strand of complementary DNA. A DNA segment is extended from tRNA based on the sequence of the retroviral genomic RNA

3. The viral R and U5 sequences are removed by RNase H.

LTR – Long Terminal Repeat

Left LTR - Redundant sequence [R]+ 5’ untranslated region (U5)

Right LTR - Redundant sequence [R]+ 3’ untranslated region (U3)

Slide 10

4. First jump: DNA hybridizes with the remaining R sequence at the 3' end.