Lecture 12

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Cell and Systems Biology
Mounir Abou Haidar

LECTURE 12THURSDAY OCTOBER VIRUS USING REVER TRANSCRIPTASESPage 87 We were studying viruses which use reverse transcriptase still in the plant system In the notes it says that plant reteroviruses are not classified anymore as reteroviruses but a bit later you will understand what the difference is True reteroviruses now the genome has to be RNA like HIV and they have to integrate into the chromosome to be classified as a true reteroviruse So cauliflour mosaic virus is a DNA virus not RNA so does not integrate into the chromosome but it uses reverse transcriptase like HIV and has its own reverse transcriptase The same is with Hepatitis B is a DNA virus uses reverse transcriptase but does not integrate with the DNA So the old classification was used in the title because some of these notes areolder than us Page 89 top diagram So cauliflower mosaic viruses is a double stranded circular DNA genome They have certain number of genes he went through them last lecture the capsule protein the reverse transcriptase which takes a chunk of the genome and the arrow indicates the orientation of transcription and the major point of this virus is that is has the 35S promoter This is the strongest promoter ever to be isolated in plants so its highly used So the virus has a capsule protein reverse transcriptase which is responsible for replication of the virus and if you understand this example you will understand how HIV replicatesSo inclusion body protein is not essential so you can remove it during recombination As any plant virus no esxception all plant viruses have to have a transport of cell to cell movement protein and this protein is responsible of allowing the DNA and protein of the viruses to go from cell to cell and remember in the plant cell they have cell wallplasmotismata for communication between cells Also this has a small protein responsible for aphid transmission aphid is a small insect which helps it get transported They have a DNA binding protein which is likely involved in replication binds to DNA and probably unwinds the DNA Supl To page 89 top figure Similar to other diagram but we will focus on thisRemember he told us the genome is nicked double stranded circular DNA but it has twonicks the diagram shows 3 but only should be 2 one has one nick on it means that the DNA is broken in one spot and the other strand has two nicks on it which means the DNA is not covalently closed circular DNA it has 1 nick on one strand and 2 nicks on the other strand Question to ask he said there should be 2 nicks and that the diagram is wrong but in the end he said there should be 1 nick on one strand and 2 nicks on the other contradiction Supl To page 89 bottom figure The virus just to see how it works the virus first enters into the cell attaches to them and ends up in the nucleus of the cell In the nucleus of the cell it does not integrate into the chromosome thats why we call it episomal which means it is in the nucleus but not integrated as part of the chromosome In the nucleus whats going to happen is that the 2 nicks are fixed to give you a perfect double stranded circular DNA Then using the DNA dependent RNA polymerase of the cell which normally transcribes the genes of the chromosomal DNA but since this one has a very
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