For running publication-quality gels, the protein samples loaded on the gels should ideally have identical running conditions. If the conditions vary, protein bands may distort during electrophoresis. Casting gels in the lab is not only time-consuming, but may also introduce errors due to variations in casting conditions. These problems can be avoided by using precast gels. Bio-Rad provides precast gels to fit various research requirements. For peptide and protein separation, they offer a wide selection of formulations of gels for SDS (sodium dodecylsulphate)-PAGE (polyacrylamide gel electrophoresis) and native PAGE. For nucleic acid (RNA, DNA) separation, they offer a selection of agarose gels. Ready Gels® are available with different combs giving variations in the number of wells and the volume that can be loaded. 10-well combs are very popular and accommodate a sample volume up to 30 microliters; 15-well combs are designed for samples of 15-20 microliters. Precast gels are also available at various concentrations of polyacrylamide or agarose, both as single percentages as well as gradients. A single percentage gel will best separate bands that are close in molecular weight within a limited range of molecular weight. If the sample contains a broad range of molecular weights, a gradient gel allows both high and low molecular weight bands to be resolved on the same gel.
Ready Gels® are shipped individually packed and can be purchased in bulk (usually at a discounted price) for labs that use them extensively. They are extremely easy to use: Just remove them from the packaging bag, cut the lower sealing band, remove the comb, load the sample and run the gel. I recommend cleaning the wells before loading the sample to eliminate unpolymerized acrylamide. Presoaking in the running buffer did not make any difference in my case. I have used these gels to separate proteins extracted from crayfish or Drosophila and then I transfer them to nitrocellulose membranes for Western blot experiments.
For difficult to obtain probes or samples, I would suggest running a mock sample or probe before running your precious sample or probe. Or at least carefully check the expiry date as I encountered situations when gels close to the expiry date did not run properly. In extremely rare situations, an entire batch of gels did not run properly even with a valid expiry date. However, the customer service replaced them at no cost. The gels have a self life of approximately 3 months from the manufacture date at 2-8ºC. I found that NuPAGE gels from Invitrogen have a better shelf life (about 12 months).
Another draw back of the Ready Gels® is that they are designed to fit the Mini-PROTEAN 3 electrophoresis cell or the discontinued Mini-PROTEAN II system as well as the Mini Trans-Blot transfer system; therefore, they cannot be used with other electrophoresis apparatus. Other precast gels from Cambrex and Diamed are compatible with most vertical electrophoresis chambers.