Question

1. Summarize DNA replication process based on the SV40 model

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Answer 1

SV40 model of DNA replication:-

• Simian virus 40 (SV40) is a polyoma virus that is found in both monkeys and humans.Its DNA has the potential to cause tumors in animals.SV40 model has been widely studied for the discoveries in eukaryotic DNA rreplication.
• The viral genome of SV40 consists of circular duplex DNA molecule. It has about 5000bp and one ori(origin of replication).
• SV40 DNA replication takes place in the nucleus of the host cell. The viral genome is complicated with histones to form a structure similar to the cellular chromatin.
• The origin consist of three distinct domain. At the centre of the origin there are four copies of simple 5bp sequence (GAGGC). This sequence is recognised by T-antigen(a viral initiation protein). SR40 T-antigen plays a key role in the initiation of viral DNA replication.
• T- complex helps in unwinding of the two strands of DNA (which is generally facilitated by ATP). The unwinding principle show that helicase activities is intrinsic to T-antigen,hence generation of replication forks.
• A protein called replication protein-A (RP-A) is required for SV40 DNA replication. They also prevents the reassociation of the unwinded strands.
• The DNA polymerase α and DNA polymerase δ are the major enzymes for SV40 DNA replication. They are correlated with cell proliferation. They serve as proof reading of 3'-5' exonuclease. The DNA polymerase α enabled the synthesis of the template DNA strand.
• Finally the two strands gets interwind,hence another copy of DNA is created. Hence this tumor virus has proved to be a good model for DNA replication.