Nucleic Acids Research, 2002, Vol. 30, No. 14 3192-3201
© 2002 Oxford University Press
Preformed hexamers of SV40 T antigen are active in RNA and origin-DNA unwinding
Medizinische Biochemie und Molekularbiologie, Universität des Saarlandes, Gebäude 44/45, D-66421 Homburg (SAAR), Germany
*To whom correspondence should be addressed. Tel: +68 41 1626020; Fax: +68 41 1626521; Email: bchsta{at}uniklinik-saarland.de
Preformed hexamers of simian virus 40 (SV40) large tumor antigen (T antigen) constitute the bulk of T antigen in infected cells and are stable under physiological conditions. In spite of this they could not be assigned a function in virus replication or transformation. We report that preformed hexamers represent the active T antigen RNA helicase. Monomers and smaller oligomeric forms of T antigen were inactive due to the lack of hexamer formation under RNA unwinding conditions. In contrast to the immunologically related cellular DEAD-box protein p68, the T antigen RNA helicase is found to act in a much more processive way and it does not catalyze rearrangements of structured RNAs. Thereby, it rather seems to resemble other virus-encoded RNA helicases, like vaccinia virus NPH-II. Surprisingly, in our hands preformed hexamers also strikingly bound to and unwound the SV40 replication origin, pointing to a possible role of preformed hexamers in the initiation step of viral DNA replication. Furthermore, we have detected an extra hexamer-specific, high-affinity T antigen ATP binding site with a very slow exchange rate constant, the function of which is discussed.
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