Figure 4. Evolution of DNA replication mechanisms from the simple asymmetric mode to the symmetric mode (or vice versa).

Figure 4

Evolution of DNA replication mechanisms from the simple asymmetric mode to the symmetric mode (or vice versa). In the fully asymmetric mode (top) that occured in RNA and DNA viruses, one strand is replicated entirely before the initiation of replication of the displaced strand. The minimal requirement of this mechanism is a DNA polymerase and a priming system. Strand displacement can be made more efficient by the recruitment of processivity factors and a helicase. In the semi-asymmetric mode (middle) a DNA primase initiates replication on the displaced strand before termination of the replication of the first (leading) strand. In the symmetric mode (bottom) coupling between primase and helicase allows the displaced strand (now the lagging strand) to be replicated together with the leading strand.

From: Origin and Evolution of DNA and DNA Replication Machineries

Cover of Madame Curie Bioscience Database
Madame Curie Bioscience Database [Internet].
Austin (TX): Landes Bioscience; 2000-2013.
Copyright © 2000-2013, Landes Bioscience.

NCBI Bookshelf. A service of the National Library of Medicine, National Institutes of Health.