TOPOISOMERASE-II FORMS MULTIMERS IN-VITRO - EFFECTS OF METALS, BETA-GLYCEROPHOSPHATE, AND PHOSPHORYLATION OF ITS C-TERMINAL DOMAIN

We present a novel assay for the study of protein-protein interactions involving DNA topoisomerase II. Under various conditions of incubatio n we observe that topoisomerase II forms complexes at least tetrameric in size, which can be sedimented by centrifugation through glycerol. The multimers are enzymatically active and can be visualized by electr on microscopy. Dephosphorylation of topoisomerase II inhibits its mult imerization, which can be restored at least partially by rephosphoryla tion of multiple sites within its 200 C-terminal amino acids by casein kinase II. Truncation of topoisomerase II just upstream of the major phosphoacceptor sites reduces its aggregation, rendering the truncated enzyme insensitive to either kinase treatments or phosphatase treatme nts. This is consistent with a model in which interactions involving t he phosphorylated C-terminal domain of topoisomerase LT aid either in chromosome segregation or in chromosome condensation.