FAST PROCEDURE TO DISTINGUISH CIRCULAR AND LINEAR DNA-MOLECULES IN PULSED-FIELD ELECTROPHORESIS

We describe here a fast procedure to identify, by Pulsed Field Gel Ele ctrophoresis (PFGE), circular DNA molecules, displaying shift mobility dependent on ethidium bromide (EtBr) concentration. Several identical DNA samples were coelectrophoresed in a multilane gel with different EtBr concentrations in each lane. Samples were run in a Contour Clampe d Homogeneous Electric Field (CHEF) or in a small CHEF (miniCHEF) equi pment for 15 or 4 h, respectively. Circular DNA molecules from the pro tozoan parasite Entamoeba histolytica were detected in a single runnin g. The circles were isolated from the gels and then their structure wa s confirmed by transmission electron microscopy. By hybridization it w as shown that the circles obtained corresponded to the ribosomal DNA e pisome.