PCR-based genome walking methods (review)

The review discusses a range of classical and modern methods used to determine the nucleotide sequence of unknown DNA regions flanking known ones. These methods are applied to decipher the regulatory regions of genes, identify integration sites of T-DNA or viruses, and so on, in cases where the use of whole-genome sequencing is not justified. To amplify a DNA segment, a binding site for a primer must be added to the end of the unknown sequence. This can be achieved either by ligating an adapter or by annealing a degenerate primer under gentle conditions, or by looping the DNA fragment so that the target region is surrounded by known sequences. The second important task is to eliminate the inevitable products of nonspecific binding of adapters or degenerate primers, which is often resolved through multiple rounds of nested PCR. Different methods vary significantly in terms of complexity, prevalence, and the availability of required reagents.