PCR is a cell-free test tube method for amplifying a target sequence of DNA. Which of the following is not required for PCR?

PCR is an in vitro method for the polymerase-directed amplification of specific DNA sequences using two oligonucleotide primers. The reaction components (e.g., template, primers, Taq polymerase,2'-deoxynucleoside 5'-triphosphates, and buffer) could all be assembled and the amplification reaction carried out by simply cycling the temperatures within the reaction tube. Ref: Feng X., Lin X., Brunicardi F.C. (2010). Chapter 15. Molecular and Genomic Surgery. In F.C. Brunicardi, D.K. Andersen, T.R. Billiar, D.L. Dunn, J.G. Hunter, J.B. Matthews, R.E. Pollock (Eds), Schwaz's Principles of Surgery, 9e.