PHOSPHORYLATION OF SERINE RESIDUES IN THE N-TERMINAL DOMAINS OF EUKARYOTIC TYPE-I TOPOISOMERASES

Eukaryotic topoisomerase I polypeptides can be partitioned into four s tructural domains. The function of the N-terminal domain, which is a t arget for serine-specific phosphorylation, has not been fully defined. The number of serine residues in the N-terminal domain of topoisomera se I from different species is inversely proportional to the number of charged amino acids in this region of the protein. The significance o f this correlation is discussed in terms of a possible role for serine -specific phosphorylation in the activity of the enzyme.