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.
Reverse Transcriptase also known as RNA directed DNA Polymerase
- DNA Nucleotidyl transferase (RNA directed)
Reverse Transcriptase was discovered by Howard Temin and Baltimore in 1970 independently
- shared Nobel Prize in Physiology or Medicine in 1975 for their discovery.
M-MLV (Moloney Murine Leukemia Virus)
AMV (Avian Myeloblastosis Virus)
Reverse Transcriptase enzyme includes two activity: DNA polymerase and RNase H
Packaging into virus ; budding
Typical retrovirus has three or four genes.
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
Like DNA polymerase, Reverse transcriptase requires primers.
tRNA of the host is Primer
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)
4. First jump: DNA hybridizes with the remaining R sequence at the 3' end.