The highly basic ribosomal protein L41 interacts with the β subunit of protein kinase CKII and stimulates phosphorylation of DNA topoisomerase IIα by CKII

Abstract

Protein kinase CKII (CKII) is a heterotetramer composed of two catalytic (α or α') and two regulatory (β) subunits. Using the yeast two-hybrid system, we have identified the highly basic, ribosomal protein L41 as a cellular protein capable of interacting with the β subunit of CKII. We show, furthermore, using purified proteins, that L41 protein and CKIIβ associate directly in vitro. L41 protein is not a substrate for CKII phosphorylation, and it does not stimulate CKII activity with either β-casein or synthetic peptide substrate (RRREEETEEE). However, L41 protein stimulates the phosphorylation of DNA topoisomerase IIα by CKII by 2.5 times. Additionally, L41 protein enhances the autophosphorylation of CKIIα. The data indicate that L41 protein associates with CKII and can modulate its activity toward a specific substrate or substrates. The direct interaction of CKIIβ with ribosomal proteins also suggests that CKIIβ itself or CKII holoenzyme may be involved in ribosome assembly or translational control.