Abstract: The sensitivity and specificity of polynucleotide synthesis is increased by protecting the 3′-end of an oligonucleotide used as a primer in the synthesis of the polynucleotide. Protection of the 3′-end of an oligonucleotide prevents non-specific chain elongation. Removal of blocking group an elevated temperature, using a thermostable enzyme, permits template-specific polynucleotide synthesis. The present invention also provides oligonucleotides with a 3′ end protected by a blocking group and a thermostable enzyme capable of removing the blocking group at an elevated temperature. The compositions and methods of the invention are very useful in a variety of techniques for DNA/RNA amplification and analysis, including medical genetics research and diagnosis, pathogen detection, forensic, and animal and plant genetics applications, among others.