ADP‐ribosylation of nucleolar proteins in HeLa tumor cells

Abstract
ADP‐ribosylation reactions in nucleoli of exponentially growing HeLa cells were studied. Isolated nuclei or nucleoli were labeled with 32P‐NAD; then the nucleolar proteins were analyzed by 1‐dimensional and 2‐dimensional polyacrylamide gel electrophoresis (PAGE) and modified proteins were detected by autoradiography. The labeled nucleolar proteins were also chromatographically fractionated on DEAE‐cellulose. Electrophoretic analysis of total nucleolar and chromatographically purified proteins revealed that besides nuclear ADP‐ribosyltransferase and histones two characteristic nucleolar phosphoproteins numatrin/B23 and nucleolin/C23 were modified by ADP‐ribosylation.