Sedimentation coefficients of replicating and crosslinked DNA

The sedimentation coefficients of branched and cyclic replicating DNA structures have been calculated taking into account both chain stiffness and excluded volume effects. For branched DNA, the calculated ratio S⁰(α)/S⁰(0) of the sedimentation coefficient at degree of replication α to that at α = 0 increases from 1.000 to 1.331 as α goes from 0 to 1. For cyclic replicating DNA, S⁰(1)/S⁰(0) = 1.517. The considerable difference between these two ratios for α = 1 suggests that the two types of replicating structures may feasibly be distinguished by sedimentation velocity studies, A similar calculation has been made of the sedimentation coefficient of singly cross-linked DNA under denaturing conditions, as a function of placement of the crosslink. In 0.195M Na⁺, the ratio S⁰(α)/S⁰(0) varies from 1.000 at α = 0 to 1.124 at α = 0.5, where α is the fractional distance of the crosslink from the end of the chain.