Patent ID: 7217514

Claim:
An in vitro method of making circular sequence variants from one or more circular heteroduplex polynucleotides wherein said heteroduplex polynucleotides have at least two non-complementary nucleotide base pairs separated by complementary nucleotide base pairs, said method comprising: a) preparing the one or more circular heteroduplex polynucleotides; b) sequentially or concurrently combining said circular heteroduplex polynueleotides with purified enzymes wherein the enzymes consist essentially of an effective amount of a mismatch recognizing and mismatch directed endonuclease CEL I, T4 DNA polymerase, and E. coli DNA ligase; c) allowing sufficient time for the percentage of complementarity and diversity in a population of polynucleotides to increase such that one or more circular sequence variants are made which are different from the circular heteroduplex polynueleotides, and which contain a partial sequence matching each polynucleotide in the circular heteroduplex polynueleotides; d) separating said sequence variants from the polynucleotides which make up the circular heteroduplex polynucleotide; and e) recovering said circular sequence variants, wherein at least one circular sequence variant has a different desired functional property from the polynucleotides in said one or more circular heteroduplex polynucleotides.