MURINE POLYOMAVIRUS AND SIMIAN-VIRUS-40 LARGE T-ANTIGENS PRODUCE DIFFERENT STRUCTURAL ALTERATIONS IN VIRAL ORIGIN DNA

Murine polyomavirus (Py) and simian virus 40 (SV40) encode homologous large T antigens (T Ags) and also have comparable sequence motifs in t heir core replication origins. While the ability of SV40 T Ag to produ ce specific distortions,within the SV40 core replication origin (ori) in a nucleotide-dependent fashion has been well documented, little is known about related effects of Py T Ag on Py ori DNA. Therefore, we ha ve examined viral origin DNA binding in the presence of nucleotide and the resulting structural changes induced by Py and SV40 T Ags by DNas e I footprinting and KMnO4 modification assays. The structural changes in the Py ori induced by Py T Ag included sites within both the AIT a nd early side of the core origin region, consistent with what has been shown for SV40. Interestingly, however, Py T Ag also produced sites o f distortion within the center of the origin palindrome and at several sites within both the early and late regions that flank the core ori. Thus, Py T Ag produces a more extensive and substantially different p attern of KMnO4, modification sites than does SV40 T Ag. We also obser ved that both T Ags incompletely protected and distorted the reciproca l ori region. Therefore, significant differences in the interactions o f Py and SV40 T Ags with ori DNA may account for the failure of each T Ag to support replication of the reciprocal ori DNA in permissive cel l extracts.