Simian virus 40 large T antigen DNA helicase. Characterization of the ATPase-dependent DNA unwinding activity and its substrate requirements.
The ATPase of SV40 large T antigen (T antigen) which is essential for the replication of SV40 minichromosomes was recently shown to be functionally related to a newly discovered DNA helicase activity. The T antigen helicase unwinds DNA duplices of several kilobase pairs in a reaction depending on the presence of hydrolyzable ribo- or deoxyribonucleoside triphosphates. The in vitro rate of movement through duplex DNA was found to be about 100 base pairs/min at 37 degrees C. For DNA unwinding, T antigen requires a 3'-single strand extension of a partially double-stranded substrate and invades the double strand section processively, in a 3' to 5' direction. The minimum length of the single-stranded tail was determined to be less than 5 nucleotides. Unwinding studies in the presence of the Escherichia coli single strand-specific DNA-binding protein and competition experiments indicate that T antigen helicase binds preferentially at the single-stranded/double-stranded DNA junction. This DNA structure is therefore proposed to serve as an entry site for the T antigen helicase. Previously reported data suggest that T antigen is the replicative helicase of the SV40 minichromosome. The results presented here are consistent with these findings and imply that T antigen migrates actively and processively along the template for the leading strand.
Wiekowski
M
M
Fakultät für Biologie, Universität Konstanz, Federal Republic of Germany.
Schwarz
M W
MW
Stahl
H
H
D000952:Antigens, Polyomavirus Transforming; D004264:DNA Topoisomerases, Type I / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000378:metabolism; D004926:Escherichia coli / Q000378:metabolism; D007700:Kinetics; D013539:Simian virus 40 / Q000201:enzymology* / Q000276:immunology; D013379:Substrate Specificity
D000952:Antigens, Polyomavirus Transforming; D004268:DNA-Binding Proteins; D004264:DNA Topoisomerases, Type I