Recombinant CEL I, SP Iwt and SP IH135A nucleases' action on a multi-mismatch PCR substrate. Simultaneous detection of three SNPs in one 490 bp PCR product of BRCA1 gene derived from a heterozygous patient. The DNA strand labeled with Cy5.5 fluorescent dye is shown. Unprocessed chromatograms are shown in full-scale display. (A) Molecular weight standards, Beckman Coulter. (B) Native CEL nuclease purified from celery, pooled fractions after MonoQ step . (C) Recombinant CEL I. (D) SP Iwt. (E) SP IH135A. The 70, 300 and 305 nt long CEL I reaction products correspond to BRCA1 nucleotide substitutions 2430 C → T, 2201 T → C and 2196 G → A, respectively.