Cloning of the ppu21IM gene using a in vivo selection method.

A genetic system enabling the in vivo selection of genes encoding the DNA-modifying enzymes was developed. A gene library is transformed into a strain harboring the restriction-modification (R-M) system which a recognition sequence is a subset of the target sequence of the DNA methyltransferase (MTase) to be cloned. If the residing MTase is temperature sensitive, the inability of transformants to grow at 42 degrees C provides a simple and convenient procedure for the isolation of new MTase-encoding genes. The feasibility of this procedure has been demonstrated by the isolation of the ppu21IM gene from a Pseudomonas putida RFL21 gene library.