Georgetown University

Gordon B Collier

Jack G Chirikjian

John F Connaughton

The present invention relates to a method for cloning genes that encode restriction endonucleases by altering the level of a methyl donor co-factor of a DNA methyltransferase that protects the DNA of a host cell from damage by a restriction endonuclease. The method can be used to screen entire DNA libraries en masse to identify clones that encode restriction enzymes by growing one library replicate under high or normal methyl donor conditions to protect host DNA and a second library replicate under low methyl donor conditions allowing DNA damage from the active restriction endonuclease. Clones that encode a restriction enzyme are identified by decreased growth or color produced in response to double stranded DNA damage under the low methyl donor conditions. Colorimetric methods useful in the invention can use SOS-sensitive promoters operably linked to .beta.-galactosidase, which detect DNA damage.

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Washington, DC, United States of America

Gordon B Collier