4 PCR reactions were concentrated to 15 ml using microcon-30 micro concentrators (Millipore). Concentrated PCR amplicons were digested separately with Tsp509I and NsiI (New England Biolabs Inc.). Digestion was carried out in 10 mL volume, using reaction conditions specified by the manufacturer. Separation of DNA fragments was carried out in a GeneGel Excel 12.5 (T 12.5%, C 2%) (Amersham Pharmacia Biotech). The electrophoresis was carried out on a GenePhor (Amersham Pharmacia Biotech). DNA restriction fragments were visualized by silver staining using the method of Heuskeshoven and Dermick