Purification of a group of HeLa nuclear proteins that bind to a regulatory element (-1430/-1327) of the human proliferating cell nucleolar protein P120 gene.

A group of proteins was purified from HeLa nuclear extract by DNA affinity chromatography which bind to an important regulatory element (-1430/-1327) of the P120 gene. The DNA binding activity was enriched 1075 fold. By silver staining three major polypeptides (50, 40, 37 kDa) were detected in the purified fraction. The band shift assay and the southwestern assay showed that the 50 kDa protein (P50) binds to the F1 (-1430/-1327) DNA fragment. The binding specificity of the group of proteins with F1 DNA in the presence of non-specific competitor DNA is much higher than that of P50 alone. On the basis of molecular weight and specific antibody binding, the 37 kDa protein appears to be the B23 nucleolar protein.