Gene walking using sequential hybrid primer polymerase chain reaction.

We developed a simple and robust method for removing nonspecific amplification produced during gene walking with a gene-specific primer and a degenerate primer. The primary walking polymerase chain reaction (PCR) was followed by two or three PCR rounds, each incorporating a low concentration of a reverse hybrid primer, where the 3' end was bound to a target sequence generated in the preceding PCR round and the 5' end was a new sequence that generated a target sequence for the next PCR round. The low concentration of the hybrid primer and the extent of amplicon stem-loop formation inhibited nonspecific amplification and enabled successful walking along three genes.