Rolling circle replication requires single-stranded DNA binding protein to avoid termination and production of double-stranded DNA

In rolling circle replication, a circular template of DNA is replicated as a long single-stranded DNA concatamer that spools off when a strand displacing polymerase traverses the circular template. The current view is that this type of replication can only produce single-stranded DNA, because the only 3'-ends available are the ones being replicated along the circular templates. In contrast to this view, we find that rolling circle replication in vitro generates large amounts of double stranded DNA and that the production of single-stranded DNA terminates after some time. These properties can be suppressed by adding single-stranded DNA-binding proteins to the reaction. We conclude that a model in which the polymerase switches templates to the already produced single-stranded DNA, with an exponential distribution of template switching, can explain the observed data. From this, we also provide an estimate value of the switching rate constant.