Topoisomerase in DNA Replication

(Lodish et al., 2000, Section 12.3 )

Type I topoisomerases relax DNA by nicking one strand, unwinding, and then closing the duplex DNA (Fig. 12.14).

Type II topoisomerases change DNA topology by breaking and rejoining double-stranded DNA (Fig. 12.16).

Unwinding of parental DNA strands during replication and transcription causes positive supercoiling (Fig. 12.18).

In E. coli Topo II relieves this stress.
In yeast both Topo I and II can relieve both positive and negative supercoiling.

Topoisomerase II can also separate concatamers (Fig. 12.16) that form at the end of circular DNA replication (Fig. 12.19).

Linear DNAs have Topoisomerase II attached where DNA binds the protein scaffolding and plays a role in relieving tornsional strain during replication.

Activity

Quiz

References:
Lodish, H., Berk, A., Zipursky, S.L., Matsudaira, P., Baltimore, D., Darnell, J., 2000, Molecular Cell Biology, 4th Ed., W.H. Freeman and Company, NY, New York. ISBN 0-7167-3136-3.