Abstract: A method is disclosed for in vitro mutagenesis of a target DNA sequence which generates mutants containing a single randomly-located region in the target sequence with random substitution mutations. The method includes the production of a supply of a template for the target sequence and random primers having differing 3'--OH termini. At least two nucleotides are added randomly to the primers to produce modified random primers, some of which contain at least one mismatch with respect to the template. The modified random primers are employed with the supply of the sequence to polymerize from the 3'--OH terminus of the modified random primer along the template to biologically fix mutations resulting from mismatched bases and produce molecules having a double-stranded region containing a mutant strand. The molecules are transferred into the host organisms to cause at least some of the mutant strands to be replicated in the host organism to produce mutant DNA sequences.

Abstract: A four-walled, open-topped container having a lid is disclosed in which the lid is insertable into the container for storage along and against one wall of the container. The lid for the container is generally planar and has a trapezoidal shape and the four walls of the container are generally planar, are interconnected, and are joined to a bottom. A rim for engaging the lid is defined by the upper ends of the four walls. The rim is trapezoidal in shape to conform to the lid and has long and short parallel opposed sides and two converging opposed sides. The four walls converge inwardly from the rim to the bottom to a sufficient degree to permit a container to nest within a like container. In addition, the convergence of the walls which define the opposed converging sides of the rim is appropriate to permit the lid to be inserted into the container along and against the wall defining the long parallel side of the rim.