Reagents and methods of pcr

In a reaction mixture for a primer-dependent DNA amplification reaction including primer extension by a DNA polymerase for amplifying at least one DNA target sequence, said reaction mixture including at least one primer pair, a DNA polymerase and dNTP's, the improvement comprising including in the reaction mixture prior to the start of amplification at least one double-stranded oligonucleotide additive that has a hybrid length of 6-50 nucleotides long, that is at least fifty percent double-stranded at 32° C., that has terminal regions on each of its strands and includes 1-4 modifying groups, each covalently attached to a different terminal region, said modifying groups being polycyclic moieties that do not have bulky portions that are non-planar, wherein said at least one double-stranded oligonucleotide additive is included at a concentration relative to the concentration of said DNA polymeras that is effective for at least one of the functions of suppressing mispriming, increasing polymerase selectivity against hybrids having recessed 3′ terminal sequences that are not perfectly complementary, increasing polymerase selectivity against hybrids having recessed 3′ terminal sequences that are AT-rich, reducing scatter among replicate reactions, inhibiting polymerase 5′ exonuclease activity, and inhibiting polymerase activity;

• provided that, if the additive is a primer or detection probe for any target sequence, it includes at least three modifying groups.