nucleolar organization region (NOR)-associated protein, producing a dark region wherein the silver is deposited and denoting the activity of rRNA genes within the NOR. Human chromosomes 13, 14, 15, 21, and 22 have NORs, which increase the silver stain activity by at least 50 times. Genomic and proteomic analysis Silver staining is used to stain gels. The silver stain of proteins in Agarose gels was developed in 1973 by Kerenyi and Gallyas. Later it was adapted to polyacrylamide gels used in SDS-PAGE, and also for staining DNA or RNA. The glycosylations of glycoproteins and polysaccharides can be oxidised by a 1-hour pre-treatment with 0.1% periodic acid at 4 °C, which improves the binding of silver ions and the staining result. First, the proteins are denatured in the gel by a fixative solution of 10% acetic acid and 30% ethanol and precipitated, at the same time the detergent (mostly SDS) is extracted. The diffusion of the proteins is thus significantly reduced. After repeated washing with water, the gel is incubated in a silver nitrate solution. Silver ions bind to negatively charged side chains of the proteins. Excess silver ions are then washed off with water. In the final development step, the silver ions are reduced to elemental silver by addition of alkaline formaldehyde. This stains the sites where proteins are present, brown to black. The intensity of the staining depends on the primary structure of the protein. Furthermore, the cleanliness of the vessels used and the purity of the reagents influence the silver stain. Common artifacts in silver stained gels are bands of keratin in the ranges of 54-57 kDa and 65-68 kDa as a contamination of the sample prior to the electrophoresis. Methenamine silver stains There are several silver stains incorporating methenamine, including: Grocott's methenamine silver stain, used widely as a screen for fungal organisms. Jones' stain, a methenamine silver-Periodic acid-Schiff that stains for basement membrane, availing to view the "spiked" GBM associated with membranous glomerulonephritis. Gallery References External links Hempelmann E. SDS-Protein PAGE and protein detection by silverstaining and immunoblotting of Plasmodium falciparum proteins. in: Moll K, Ljungström J, Perlmann H, Scherf A, Wahlgren M (eds) Methods in Malaria Research, 5th edition, 2008, 263-266 Electron microscopy stains Genetics techniques Staining