An open reading frame DNA vector is presented having a promoter-translation start region, and adjacent thereto and downstream therefrom, a first coding segment having a start codon, a second coding segment coding for detectable protein, and an insertion region between said first and second coding regions having an insertion site and being of such length that the first and second coding segments are not in reading frame phase with each other. A method for the cloning and positive selection of a DNA segment having an open reading frame is also presented, as well as a tribrid protein wherein each terminal region and the mid-section is derived from a different gene, and a method of identifying and quantifying a protein or polypeptide without regard to its structure or biological function by using a DNA segment coding for said protein or polypeptide as the mid-section of the tribrid protein.