Southern and Northern blot fixing by microwave oven.

Southern and Northern blot techniques are powerful procedures for studying gene structure and function. These methods involve the separation of nucleic acids according to size on an agarose or polyacrylamide gel and subsequent transfer of the nucleic acid to suitable nitrocellulose or nylon-based membranes. DNA or RNA molecules bound to the membrane are then fixed and hybridized with a radioactive probe, specific for the gene under study. The fixing step is particularly important for quantitatively reproducible results, especially if membranes are to be rehybridized several times. The traditional fixing procedure involved baking the membrane for 2 h at 80°C (1). More recently, it has been shown that efficient cross-linking of nucleic acids to the membrane could be obtained by 30 s to 3 min exposure of UV irradiation (2). Earlier studies described the use of a microwave oven to fix bacterial colonies to nylon membranes (3) or to fix DNA within paraffin tissue blocks (4). We demonstrate here that a 2 min treatment of Southern or Northern blots in a microwave oven efficiently fixes nucleic acids to nylon membranes which can withstand repeated reuse in hybridization reactions.