Distribution of DNA replication origins between matrix-attached and loop DNA in mammalian cells

Using a previously developed procedure (Gencheva et al. [1996] J Biol Chem 271:2608-2614), we isolated a DNA fraction consisting of short fragments or iginating from the regions of initiation of DNA synthesis from exponentiall y growing Chinese hamster ovary cells. This fraction arbitrarily designated as "collective origin fraction" was labeled in vitro and used to probe the abundance of origin containing sequences in preparations of matrix-attache d and loop DNA isolated by two different procedures from Chinese hamster ov ary cells. Alternatively, an individual DNA replication origin sequence - a 478-bp long DNA fragment located at about 17-kb downstream of the dihydrof olate reductase gene - was used to probe the same matrix-attached and loop DNA fractions. The results with both the collective and individual DNA repl ication origins showed that there was random distribution of the origin seq uences between DNA attached to the matrix and DNA from the loops. (C) 2001 Wiley-Liss, Inc.