Endogenous protein kinase activity in nuclear RNP particles from HeLa cells.

Abstract

To elucidate the mechanisms which achieve and regulate the transport from the nucleus to the cytoplasm of those sequences of heterogeneous nuclear RNA (HnRNA) destined to become cytoplasmic mRNA, we have started a systematic investigation of the proteins associated with these RNA species in the form of the so-called ‘RNP particles’. The general occurrence of such ribonucleoprotein complexes in eukaryotic cells is widely recognised although they have only recently been described in HeLa cells1,2. The occurrence of phosphorylated proteins in rat brain nuclear particles3, together with the observation that mRNA release from adenovirus-infected KB cell nuclei in vitro is an ATP-dependent process4, has prompted a search for protein kinase activity in HeLa nuclear RNP particles. The role of protein phosphorylation in the regulation of enzyme activity is now recognised5 and we have observed such an activity which does not require the addition of exogenous substrates like histones. The endogenous protein substrates present in HeLa nuclear RNP particles have also been characterised.