STIMULATION OF CALF THYMUS DNA-POLYMERASE ALPHA-ACTIVITY BY NUCLEOLARPROTEIN B23

Protein B23 is a major RNA-associated nucleolar protein and putative r ibosome assembly factor which exists in at least two isoforms designat ed B23.1 and B23.2. Recently, it has been reported that B23 is copurif ied with DNA polymerase alpha-primase complex. To examine its possible role in DNA replication, the effects of B23 on DNA polymerase activit ies were investigated. B23.1 purified from rat Novikoff hepatoma ascit es cell nucleoli stimulated the activity of DNA polymerase a by as muc h as 3-to 4-fold in a dose-dependent manner, while it showed little ef fect on the activities of DNA polymerases beta, gamma, and primase. Ra t recombinant B23.1 showed the same stimulation as that of B23.1 from Novikoff cells. In contrast, isoform B23.2 showed no effect on the act ivity of DNA polymerase alpha, suggesting that C-terminal region of B2 3.1 is important in its activity in the stimulation of DNA polymerase alpha. (C) 1994 Academic Press, Inc.