Many bacteriophages and eukaryotic viruses, which share little sequence similarities, have icosahedral protein capsids containing their genetic materials. Generally, an icosahedral viral capsid is assembly of 12 pentamers and a certain number of hexmers of the major capsid protein, following Caspar and Klug¡¯s quasi-equivalence rule. The arrangement of these pentamers and hexmers is characterized by the triangulation (T) number. Questions arise whether viruses have evolved from a few common ancestors, and how the assembly of the icosahedral capsids has been regulated to achieve a defined capsid size and geometry. I present studies of the capsids of several large icosahedral bacteriophages, which broaden our understanding of the regulation of viral capsid assembly.
Bacteriophage SPO1 may share common ancestry with herpesvirus, according to the similarities in their T numbers and in the asymmetric molecules slightly off the local three-fold symmetry positions on the outer surface of both capsids. However, the cryo-EM structure of the SPO1 capsid assembled from the uncleaved major capsid protein show that, unlike the herpesvirus asymmetric molecule, the SPO1 asymmetric protein may not be required for the initial procapsid assembly, suggesting that the two asymmetric molecules may have different origins. Phage P1 is excellent for studying size determination in viral capsid since it produces virions of three sizes. The cryo-EM structures of the three capsids and internal capsid proteins identified suggests a control mechanism for P1 capsids, in which the DarA protein functions as a semi-scaffolding protein to assist the assembly of the P1 big capsid. Jumbo phages have been rarely studied. The structural studies on four jumbo phages showed their T numbers. N3, PAU and 121Q are the first T = 19, 25 and 28 viral capsids found. These results suggest that T-numbers larger than 16 may generally be allowed.
| Identifer | oai:union.ndltd.org:PITT/oai:PITTETD:etd-12082009-150454 |
| Date | 24 June 2010 |
| Creators | Hua, Jianfei |
| Contributors | James Conway, PhD, Michael Cascio, PhD, Roger Hendrix, PhD, Peijun Zhang, PhD |
| Publisher | University of Pittsburgh |
| Source Sets | University of Pittsburgh |
| Language | English |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://etd.library.pitt.edu/ETD/available/etd-12082009-150454/ |
| Rights | unrestricted, I hereby certify that, if appropriate, I have obtained and attached hereto a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, dissertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee. I hereby grant to University of Pittsburgh or its agents the non-exclusive license to archive and make accessible, under the conditions specified below, my thesis, dissertation, or project report in whole or in part in all forms of media, now or hereafter known. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also retain the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report. |
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