A – Non-radioactive PCR-SSCP analysis of VHL exon 3; T – altered mobility observed in a tumor sample, relative to the normal control N. B – Ethidium bromide-stained polyacrylamide gel of BstZ17 I restriction digestion. Lane 1 – peripheral venous blood, Lane 2 – renal cell carcinoma, Lane 3 – non tumoral tissue from kidney, Lane 4 – thyroid metastases, M – denotes the lane containing the pUC Mix Marker 8 (Fermentas, Burlingyon, Canada). For the wild allele, restriction digestion produces bands of 212 and 59 bp. The mutation abolishes the restriction site and the mutant allele corresponds to a 271 bp band. C and D – Tumour DNA sequence in the VHL codon 156 region of cloned exon 3 amplicons. As a consequence of the 680 delA, a premature stop codon appears in the mutant allele.