A variation of the PCR technique, similar to ligation-mediated PCR, that is applied to double-stranded DNA fragments for which the sequence at only one end of the gene is known. The technique allows amplification of a complete sequence of a gene when only the N-terminal sequence of a protein is known. A short polynucleotide of known sequence is ligated to the 3'-ends of the double-stranded DNA so that a primer complementary to it can be added, along with the primer determined from the partial protein sequence.