The phosphoform of the regulatory subunit RII of cyclic AMP-dependent protein kinase possesses intrinsic topoisomerase activity

Abstract

The phosphoform of the type II regulatory subunit (phospho-RII-cAMP) of cAMP-dependent protein kinase from rat liver was found to possess intrinsic topoisomerase activity towards several DNA substrates such as φX174, pBR322, SV40, and M13. Like the type I topoisomerases from several eukaryotic cells, phospho-RII-cAMP can relax both positive and negative superhelical turns of φX174 DNA. Topological isomers with a decreasing number of superhelical turns can be identified as transient products. Conditions under which phospho-RII-cAMP relaxes superhelical φX174 DNA lead to transient formation of a DNA-phospho-RII-cAMP complex via DNA strand breakage and covalent attachment of the DNA to a tyrosine residue of phospho-RII-cAMP via a phosphodiester bond. The topoisomerase activity of phospho-RII-cAMP depends on the presence of cAMP and is altered by changes in the degree of phosphorylation of RII. Both dephosphorylation and removal of cAMP from phospho-RII-cAMP abolish its topoisomerase activity. © 1985.