The article describes a modified PCR method to introduce random point mutations into cloned genes, aiming to reduce the fidelity of Taq polymerase without significantly decreasing amplification efficiency. The method was used to mutagenize the gene encoding the Tetrahymena ribozyme, achieving a mutation rate of 0.66% ± 0.13% per position per PCR. The mutations were randomly distributed throughout the amplified sequence, following a Poisson distribution. The authors compared this method to other mutagenesis techniques and found it to be more efficient and less biased than methods using chemical mutagens or nucleotide analogues. They also tested various reaction conditions and identified a preferred condition that resulted in a low mutation rate (0.66% ± 0.13%) and no strong sequence bias. The study highlights the potential of PCR mutagenesis for generating mutant libraries and screening for desirable phenotypes.The article describes a modified PCR method to introduce random point mutations into cloned genes, aiming to reduce the fidelity of Taq polymerase without significantly decreasing amplification efficiency. The method was used to mutagenize the gene encoding the Tetrahymena ribozyme, achieving a mutation rate of 0.66% ± 0.13% per position per PCR. The mutations were randomly distributed throughout the amplified sequence, following a Poisson distribution. The authors compared this method to other mutagenesis techniques and found it to be more efficient and less biased than methods using chemical mutagens or nucleotide analogues. They also tested various reaction conditions and identified a preferred condition that resulted in a low mutation rate (0.66% ± 0.13%) and no strong sequence bias. The study highlights the potential of PCR mutagenesis for generating mutant libraries and screening for desirable phenotypes.