Abstract: Detection of mutations in a lacZ gene including lacZ operator sequence functioning as marker gene located in a plasmid whereof one or more copies are introduced into the DNA of a mammal or of a mammalian cell, by isolating the DNA, cutting the plasmid out of the DNA, picking up the plasmid DNA with solid particles to which a lacZ operator binding material is bound, again releasing the plasmid from the solid particles after isolation and subsequently circularizing the plasmid, transforming a host restriction-negative, lacZ-negative and galE-negative bacterial host with the plasmid and separating transformants with mutated lacZ gene which grow on a lactose-containing medium from transformants with a non-mutated lacZ gene which do not grow on such a medium. A transgenic mammal model for mutation analysis.

Abstract: The invention relates to a process for the rescue and cloning of a DNA sequence wherein a vector containing said DNA sequence is multiplied in a suitable bacterial host. As the bacterial host, a bacterial strain which is incapable of host restriction is used, such as an Escherichia coli C strain. Preferably, a bacteriophage vector which is a suitable cloning vehicle for the bacterial host concerned is used as the vector, the step of in vitro packaging into phage coats being performed by means of a phage packaging extract obtained from a bacterial strain which is incapable of host restriction.