Actin in transcription

Abstract

Actin is one of the most abundant proteins in eukaryotic cells. For many years, its presence in the nucleus has been considered an artefact, and the validity of the many reports published on nuclear actin has been questioned (reviewed by Pederson & Aebi, 2003). However, evidence has emerged in recent years supporting the direct functional involvement of actin, and of nuclear myosin 1 (NM1), in transcription. First, β‐actin is associated with SWI/SNF‐like chromatin‐remodelling complexes of the BAF type in mammalian cells, and β‐actin and other actin‐related proteins have subsequently been identified as components of other chromatin‐remodelling complexes (reviewed by Olave et al , 2002; Bettinger et al , 2004). Second, NM1 colocalizes with RNA polymerase II (Pol II), and antibodies against NM1‐β co‐immunoprecipitate Pol II and inhibit transcription in vitro (Pestic‐Dragovich et al , 2000). Third, studies in a variety of organisms have revealed that β‐actin interacts directly with some proteins from the heterogeneous nuclear ribonucleoprotein (hnRNP) complexes (Percipalle et al , 2002, and references therein). The association of actin with messenger‐RNA‐binding proteins is of functional importance, as has been shown by experiments using the dipteran Chironomus tentans . These studies have shown that disruption of the interaction between actin and the pre‐mRNA‐binding protein hrp65 by a competing peptide blocks Pol II transcription at the elongation level (Percipalle et al , 2003). An interaction between actin and human hnRNP U …