Abstract: Process for the preparation of a deletion fragment from a target nucleic acid, the target having a region of known nucleotide sequence identical to one terminus of the deletion fragment. In the process, the target nucleic acid is provided as a single stranded molecule. A terminus primer which is homologous to the region of known nucleotide sequence, and a set of deletion primers each of which has a fixed site region, a spacer region and a tail are also provided. The set of deletion primers contain a mixture of oligonucleotides which have homologous fixed site regions and homologous tails, and which collectively have all four bases at each nucleotide position in essentially all combinations thereof in their spacer regions. The single strands are treated with the terminus primer and the set of deletion primers to form a primer extension product wherein the target nucleic acid is used as a template.

Abstract: A test tube rack holder for supporting a test tube rack on a rotary shaker, the holder comprising a base with a platform mounted on the base. A first side bar projects outwardly from the platform and a second side bar projecting outwardly from the platform generally parallel to the first side bar, the second side bar being laterally moveable with respect to the first side bar and defining a space on the platform between the interior sides of the side bars for receiving a test tube rack. The second side bar can be secured relative to the first side bar to fix the distance between the side bars to accommodate a test tube rack. A sheet of resilient material having first and second edges is secured at one edge to the holder exteriorly of the side bars and releasably secured at the other edge to the holder exteriorly of the side bars to retain a test tube rack on the platform between the side bars.