  Enzymatic ligation is essential for the synthesis of long DNA. However, the
number of ligated products exponentially decays as the DNA synthesis proceeds
in a random manner. The controlling of ligation randomness is of importance to
suppress exponential decay and demonstrate an efficient synthesis of long DNA.
Here, we report the analysis of randomness in sequential DNA ligations, named
qPCR-based STatistical Analysis of Randomness (qPCR-bSTAR), by a probability
distribution of ligated DNA concentration. We show that the exponential decay
is suppressed in a solution of another polymer and DNA ligation is activated at
an optimal crowded condition. Theoretical model of kinetic ligation explains
that intermolecular attraction due to molecular crowding can be involved in the
optimal balance of the ligation speed and the available ligase. Our finding
indicates that crowding effects enhance the synthesis of long DNA that retains
large genetic information.
