Abstract: Provided are lacZ&agr; gene fragments which have been modified to introduce multiple restriction enzyme sites. Vectors according to the present invention include at least one promoter operatively linked to a DNA sequence encoding lacZ&agr;(&agr;-peptide); multiple cloning sites cleavable by distinct restriction enzymes which have been introduced within a lacZ coding sequence from and including the codon for amino acid 8, and in the lacZ coding sequence downstream of the codon for amino acid 8, in forming the modified lacZ&agr; coding sequence; and a replicon. Also provided are methods of using the vectors wherein a DNA molecule is cloned into at least one restriction enzyme site in the modified lacZ&agr; coding sequence, in forming recombinant vectors; introducing the recombinant vectors into competent host cells; growing the host cells in the presence of a chromogenic substrate cleavable by &bgr;-galactosidase; and screening for indicia of lac operon marker inactivation.

Abstract: Provided are lacZ.alpha. gene fragments which have been modified to introduce multiple restriction enzyme sites. Vectors according to the present invention include at least one promoter operatively linked to a DNA sequence encoding lacZ.alpha. (.alpha.-peptide); multiple cloning sites cleavable by distinct restriction enzymes which have been introduced within a lacZ coding sequence from and including the codon for amino acid 8, and in the lacZ coding sequence downstream of the codon for amino acid 8, in forming the modified lacZ.alpha. coding sequence; and a replicon. The vector may further comprise one or more additional features useful for protein expression and other molecular manipulations. Also provided are methods of using the vectors wherein a DNA molecule is cloned into at least one restriction enzyme site in the modified lacZ.alpha.