The preparation of control samples containing specific types of mutations is a necessary step for application and evaluation of new molecular biological methods in modern laboratory cancer diagnostics. The aim of the study was to prepare control samples with mutation in codon 12 of the K-ras gene for the development of PCR methods for detection of K-ras mutations in human colorectal cancer. Normal nucleotide sequence is GGT (code for glycine) in codon 12. Targeted PCR mutagenesis for forming GTT (valine), GAT (aspartate), TGT (cysteine), and GCT (alanine) mutations in this codon was used. The presence of mutant K-ras fragments in isolated phagemids was confirmed by DNA sequencing.

        Key words: cancer, polymerase chain reaction, cloning, sequencing, targeted mutagenesis.