Protein B23 (M.W./pI = 37 kD/5.1) is the only major protein extracted from HeLa nucleoli with 3M urea

HeLa nucleoli were isolated using the NP-40 method and subsequently extracted with 3M urea. The extract was incubated at 60 degrees C for 30 min, and precipitated proteins were removed by centrifugation. The supernatant was analyzed by one- and two-dimensional SDS polyacrylamide gel electrophoresis (PAGE). Protein B23 was the only major protein extracted from HeLa nucleoli by this procedure. Using this procedure, 1 mg of protein B23 was obtained from 2 g of HeLa cells. The purity of the extracted protein B23 was 98%, as measured by one- and two-dimensional gel electrophoresis.