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Molecular Genetics and Microbiology
Alan Cochrane

MGY378 – DNA viruses – February 27, 2012 Will not discuss baculovirue; iridoviruses; but rest, excluding hepadna, will be discussed Relative size of viruses – very different – Capsid – most are icosahedral; others are helical, complex - Pox virus does not resemble any other virion Envelope or not – small viruses are naked, no envelope - Herpes and pox are enveloped Single stranded or double stranded – all genomes are double stranded except for parvoviruses of viruses to be discussed Papova is old nomenclature – papilopma and polyomaviruses initially grouped together into one family because close resemblance – similar size, characteristics, etc – but some fundamental differences Only pox virus brings in its own RNA polymerase – life cycle in cytoplasm – others live in nucleus - Other viruses wil have exposure to DNA polymerase, - Pox does not have that exposure – need to have extra “luggage” Correlation some between size of virion and size of genome PARVOVIRUS - Large group of viruses – widespread in variety of animals - Two big subfamily – one infects vertebrates, other infects insects Parvovirus – first in vertebrate virus – no human counterpart in this subfamily - Not to be discussed Amdovirus – causes disease in mink Erythrovirus – B19 associated with disease Bocavirus – HboV1 discovered in 2005 – common in respiratory tract 1 to 4 are autonomous parvoviruses – do not need helper virus to enter cell and replicate Dependovirus – aka AAV – needs helper virus – usually adenovirus, can also be herpesvirus B19 – most ppl have antibodies against this virus – infects precursor cells - Serious issue in haemolytic anemia patients - Commonly found in heart – site of lifelong persistence perhaps? o Cardiac issues? Unsure in literature - Virus can cross placenta and infect fetus – Fifth disease – occurring towards end of B19 infection - Red rash on cheeks – resolves on its own - Immune complexes build up in joints in adult – also tends to resolve on its own Virion - Very small – smallest DNA viruses - No envelope - Small enough to fit through nuclear pore – only DNA virus able to do this Genome - Linear single stranded but ends have particular structure, called T shaped structure due to complementarity of sequence o Base paired o T shape on both ends - In autonomous viruses – only encapsidate minus strand – complementary to one used as mRNA o Both have T shaped structure but the sequences different – directionality – and proteins can distinguish the strands - AAV – encapsidate either strand – approximately equal frequency – ends are inverted terminal repeats of each other Gene expression - Genome organized into two half – one half for structural proteins o VP are the capsids - Other proteins involved in replicating genome o Rep and number Infection - Recognize cell surface receptor - Endocytosis – uptake via endosome – - Acificiation - Breaking and releasing the capsids with genome still inside - Move with aid of microtubules ot nuclear pore and enter - DNA then come out depending on virus – - Permissivity of infection determined in several ways - dsDNA used for gene expression – amplify and make more copies of viral geome - needs to be in S phase of cell cycle for all this to occur Autonomous parvoviruses - require cells to enter S phase to replicate o no method to induce cell into S phase - DNA remains in capsid until S phase starts - For AAV, needs helper virus o Could not identify particular adenovirus protein o Suggesting not a particular viral protein ne
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