  We compute for the first time the effects of excluded volume on the
probability for double-stranded DNA to form a loop. We utilize a Monte-Carlo
algorithm for generation of large ensembles of self- avoiding worm-like chains,
which are used to compute the J-factor for varying lengthscales. In the
entropic regime, we confirm the scaling-theory prediction of a power-law drop
off of -1.92, which is significantly stronger than the -1.5 power-law predicted
by the non-self-avoiding worm-like chain model. In the elastic regime, we find
that the angle-independent end-to-end chain distribution is highly anisotropic.
This anisotropy, combined with the excluded volume constraints, lead to an
increase in the J-factor of the self-avoiding worm-like chain by about half an
order of magnitude relative to its non-self-avoiding counterpart. This increase
could partially explain the anomalous results of recent cyclization
experiments, in which short dsDNA molecules were found to have an increased
propensity to form a loop.
