DNA primers, nucleotides, and polymerase are all found in a PCR reaction mix. Primers are needed to anneal to the template strand and provide an area for Taq (DNA) polymerase to bind and synthesize the complementary strand. Nucleotides are needed so that Taq polymerase has the materials to create the new strand.
However, DNA ligase is not needed in a standard PCR reaction since there is no need to ligate any DNA molecules (fix their backbones).
