Two discrete DNA replication intermediates are formed in melphalan-treated cells.

In undisturbed cells one can detect a discrete population of 10 kb DNA replication intermediates, which indicates the existence of gaps spaced about 10 kb away from each other in the newly synthesized DNA. In melphalan-treated cells one can detect both 10 kb and 20 kb DNA intermediates, indicating that in such cells the gaps present in a replicon are not filled at the same time which allows the detection of a molecule which is formed by the joining of two 10 kb DNA intermediates. In contrast in undisturbed cells it is likely that the filling of the gaps present in a replicon occurs at the same time which prevents the detection of a 20 kb DNA intermediate.