The protein composition of HeLa ribosomal subunits and nucleolar precursor particles

Using two-dimensional polyacrylamide gel electrophoresis, the protein patterns from HeLa 80S and 55S nucleolar precursor particles have been compared with those of cytoplasmic 40S and 60S ribosomal subunits. The 55S particle was found to have 21 anionic and 52 cationic proteins, including 18 large subunit ribosomal proteins. The 80S precursor pattern was identical to the 55S pattern except three anionic and four cationic proteins were absent. Of those missing cations, three were large subunit proteins. However, no small subunit ribosomal proteins were detected on either precursor. Numerous high molecular weight non-ribosomal proteins were found in both precursor particles and may correspond to a class of stable nucleolar proteins.