Characterization of a DNA-protein complex and capsomere subunits derived from polyoma virus by treatment with ethyleneglycol-bis-N,N'-tetraacetic acid and dithiothreitol

Publisher Website
Google Scholar
Abstract
Treatment of polyoma virions with ethyleneglycol-bis-N,N''-tetraacetic acid (EGTA) and dithiothreitol (DTT) at pH 8.5 resulted in the dissociation of the virions into a DNA-protein complex and individual structural capsomere subunits. The sedimentation value of the DNA-protein complex in sucrose gradients was approximately 48S, and it had a density of 1.45 g/cm3 in equilibrium CsCl gradients. Alkaline sucrose analysis of the DNA within this DNA-protein complex demonstrated that approximately 75% of the DNA is component 1. The proteins associated with the DNA were dissociated by treatment with either NaCl or the anionic detergent Sarkosyl. VP1 and the histone proteins VP4-7 were the major proteins associated with the DNA. Treatment of the DNA-protein complex with alkaline pH resulted in the specific removal of VP1. EM of the 48S DNA-protein complex demonstrated that it is a very tightly coiled structure that is slightly larger than the intact virion. Treatment of the complex with either NaCl or with pH 10.5 buffer resulted in the loss of protein and subsequent loosening of the DNA-protein complex such that the DNA could be visualized. The capsomere subunits released as a result of the EGTA-DTT treatment sedimented as 18S, 12S and 5S subunits in sucrose gradients. Electrophoretic analysis of the isolated capsomeres demonstrated that VP1, VP2 and VP3 were present in each species, although the ratios of the proteins varied. Besides the structural proteins, histones VP4-7 were predominantly associated with the 5S capsomere subunit.