Abstract
We present a novel general method for localized mutagenesis. The DNA segment to be mutagenized is inserted in the beta-galactosidase gene of a M13-lac vector, generally causing loss of beta-galactosidase function by generation of frameshifts or nonsense codons. Mutations in the inserted DNA which restore beta-galactosidase function are readily detected and analyzed. The application of this method to the promoter of an eukaryotic (Caenorhabditis elegans) tRNAPro gene has allowed the isolation of several mutants altered in transcription.