SpeakerProf. Alexander McPherson, MCDB @ UC Irvine, Host: Everett Lipman & Kevin Plaxco
Date and LocationWednesday April 13, 2016 11:00am to 12:00pm
Satellite Tobacco Mosaic Virus : Icosahedral Capsid and RNA Structure
University of California, Irvine
Satellite tobacco mosaic virus (STMV) is the second smallest icosahedral virus known. It is composed of 60 identical protein subunits enclosing a single stranded RNA genome of 1058 nucleotides that codes only for the coat protein. STMV cannot replicate in the absence of its co-infecting master virus tobacco mosaic virus (TMV), the classical rod shaped, helical virus. Some time ago we crystallized STMV in a variety of unit cells and solved its structure by X-ray diffraction. The STMV model, which includes nearly 40 % of the RNA, visible in native electron density maps, has now been refined to 1.4 A resolution, the highest, by a large measure, of any virus. In most respects, the details of the capsid are interesting but not exceptional, as they conform to expectations for icosahedral virus protein topology. The RNA, however, is exceptional in that it is organized within the virion, itself, with a remarkable degree of icosahedral symmetry. It is the RNA and its distribution within the virion that makes STMV unique, as it provides the best opportunity we have for determining the conformation of the nucleic acid in any spherical virus. As a consequence, work is progressing in several laboratories by chemical and physical means to determine, in a definitive manner, its three dimensional structure. In this lecture, the properties of the viral capsid will be reviewed, current hypotheses on the structure of the RNA presented, and the still controversial state of present research regarding its conformation discussed.