Low concentrations of tetramethylammonium chloride increase yield and specificity of PCR

Polymerase chain reaction (PCR) and its diverse technical exten-sions and developments has evolved into the method-of-choice to isolate and amplify specific segments of DNA out of a complex mixture of sequences (1). In PCR, two oligonucleotides serve as reciprocal primers flanking the DNA fragment matrix to be amplified Some simple rules help design efficient primers. Ideally, primers should be 16-26 nucleotides in length, contain 50-60% guanines and cytosines (GC) and anneal to the matrix at-55 °C (0-10°C below the Tm: temperature at wliich 50 % of the DNA molecules are denatured; 2). The numerous protocols designed for the different PCR applications almost always require an optimisation step when put into practice. We frequently undertook PCR experiments as part of our studies on the adenine and thymine (AT>rich macronuclear genome of Parameciwn primaurelia (80% AT content; 3). The low annealing temperatures required ofte