title: Circular DNA of 3T6R50 double minute chromosomes.
abstract: In pulsed field gradient gel electrophoresis (PFGE) the intact deproteinized circular DNA of Mycoplasma (800 kb) and Escherichia coli (4700 kb) remains trapped in the slot. We show here that gamma-irradiation of the DNA in agarose plugs is a convenient method to partially convert these circles into full-length linears, migrating with the expected mobility in PFGE. We have used this method to study the structure of Double Minute chromosomes (DMs) from the methotrexate (MTX)-resistant mouse cell line 3T6R50. Intact deproteinized DM DNA is immobile in these gels, but is converted into a single band of about 2500 kb by either gamma-irradiation, DNaseI in the presence of Mn2+, or restriction enzymes. We conclude that the DM DNA in 3T6R50 cells consists of a homogeneous population of 2500-kb circles.
authors.affiliation: Division of Molecular Biology, The Netherlands Cancer Institute, Amsterdam.
authors.forename: A M
authors.initials: AM
authors.lastname: van der Bliek
authors.forename: C R
authors.initials: CR
authors.lastname: Lincke
authors.forename: P
authors.initials: P
authors.lastname: Borst
mesh_terms: D000818:Animals; D002460:Cell Line; D004269:DNA, Bacterial / Q000032:analysis / Q000528:radiation effects; D004270:DNA, Circular / Q000032:analysis* / Q000528:radiation effects; D004351:Drug Resistance; D004587:Electrophoresis, Agar Gel / Q000379:methods; D004926:Escherichia coli / Q000032:analysis; D005720:Gamma Rays; D005784:Gene Amplification; D008727:Methotrexate / Q000494:pharmacology; D051379:Mice; D009174:Mycoplasma / Q000032:analysis
chemical_list: D004269:DNA, Bacterial; D004270:DNA, Circular; D008727:Methotrexate