DNA molecular weight ladders that have been electrophoresed on a 1% agarose gel and then stained for 30 minutes with a 1:10,000 dilution of SYBR® Green I nucleic acid gel stain (Cat. no. S7563, S7567, S7585). Lanes 1 and 8 contain HindIII–cut ? DNA; lanes 2 and 7, HaeIII–cut fX174 RF DNA; lanes 3 and 6, 1 kilobase pair DNA ladder (GIBCO/BRL); lane 4, 100 base pair DNA ladder (GIBCO/BRL); lane 5, EcoR-I–cut pUC19 DNA mixed with PstI–cut fX174 RF DNA. Gel staining was visualized using 254 nm epi-illumination.