Journal
PROTEIN ENGINEERING DESIGN & SELECTION
Volume 29, Issue 12, Pages 617-628Publisher
OXFORD UNIV PRESS
DOI: 10.1093/protein/gzw052
Keywords
amplification bias; in vitro evolution; iCSR; phi29 DNA polymerase; WGA
Funding
- Europe Union Structural Funds [VP2-1.3-UM-02-K-04-013]
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Compartmentalized self replication (CSR) is widely used for in vitro evolution of thermostable DNA polymerases able to perform PCR in emulsion. We have modified and adapted CSR technique for isothermal DNA amplification using mezophilic phi29 DNA polymerase and whole genome amplification (WGA) reaction. In standard CSR emulsified bacterial cells are disrupted during denaturation step (94-96 degrees C) in the first circles of PCR. Released plasmid DNA that encodes target polymerase and the thermophilic enzyme complement the emulsified PCR reaction mixture and start polymerase gene amplification. To be able to select for mezophilic enzymes we have employed multiple freezing-thawing cycles of emulsion as a bacterial cell wall disruption step instead of high temperature incubation. Subsequently WGA like plasmid DNA amplification could be performed by phi29 DNA polymerase applying different selection pressure conditions (temperature, buffer composition, modified dNTP, time, etc.). In our case the library of random phi29 DNA polymerase mutants was subjected to seven selection rounds of isothermal CSR (iCSR). After the selection polymerase variant containing the most frequent mutations was constructed and characterized. The mutant phi29 DNA polymerase can perform WGA at elevated temperatures (40-42 degrees C), generate two to five times more of DNA amplification products, and has significantly increased half-life at 30 and 40 degrees C, both in the presence or the absence of DNA substrate.
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