Actin and nuclear myosin I are associated with RNAP II and function in gene transcription

The presence of actin in the nucleus as well as its functions in various nuclear processes has been made clear in the past few years. Actin is known to be a part of chromatin-remodeling complexes BAF, which are required for maximal ATPase activity of the Brg1 component of the BAF complex. Moreover, the essential roles of actin in transcription mediated by RNA polymerases Ⅰ,Ⅱ and Ⅲ have been demonstrated recently. On the other hand, a myosin Ⅰ isoform, which contains a unique NH2-terminal extension for nucleus localization, has been specifically localized in nucleus. As is well known, myosin Ⅰ is an actin-binding protein and plays an important role in various cellular activities. Though actin and nuclear myosin Ⅰ (NM Ⅰ) have been implicated to play distinct roles in gene expression, there has been no evidence for the actin-myosin interaction that might be involved in gene transcription mediated by RNA polymerase Ⅱ (RNAP Ⅱ). Here we show evidence that both actin and NM Ⅰ are associated with RNAP Ⅱ in nucleus by using co-localization and co-IP assays, and they may act together on gene transcription. The antibodies against β-actin or NM Ⅰ can block RNA synthesis in a eukaryotic in vitro transcription system with template DNA comprising the promoter and the coding region of human autocrine motility factor receptor (hAMFR) gene; the antibodies pre-adsorbed with purified actin and NM Ⅰ have no effect in transcriptional inhibition, indicating that the inhibition of transcription by anti-actin and anti-NM I is specific. These results suggest a direct involvement of actin-myosin complexes in regulating transcription. It also implicates that actin and NM Ⅰ may co-exist in a same complex with RNAP Ⅱ and the interaction of RNAP Ⅱ with actin and NM Ⅰ functions in the RNAP Ⅱ-mediated transcription.

The presence of actin in the nucleus as well as its functions in various nuclear processes has been made clear in the past few years. Actin is known to be a part of chromatin-remodeling complexes BAF, which are required for maximal ATPase activity of the Brgl component of the BAF complex. Moreover, the essential roles of actin in transcription mediated by RNA polymerases Ⅰ, Ⅱ and Ⅲ have been demonstrated recently. On the other hand, a myosin Ⅰ isoform, which contains a unique NH2-terminal extension for nucleus localization, has been specifically localized in nucleus. As is well known, myosin Ⅰ is an actin-binding protein and plays an important role in various cellular activities. Though actin and nuclear myosin Ⅰ （NM Ⅰ） have been implicated to play distinct roles in gene expression, there has been no evidence for the actin-myosin interaction that might be involved in gene transcription mediated by RNA polymerase Ⅱ （RNAP Ⅱ）. Here we show evidence that both actin and NM Ⅰ are associated with RNAP Ⅱ in nucleus by using co-localization and co-IP assays, and they may act together on gene transcription. The antibodies against β-actin or NM Ⅰ can block RNA synthesis in a eukaryotic in vitro transcription system with template DNA comprising the promoter and the coding region of human autocrine motility factor receptor （hAMFR） gene; the antibodies pre-adsorbed with purified actin and NM Ⅰ have no effect in transcriptional inhibition, indicating that the inhibition of transcription by anti-actin and anti-NM b is specific. These results suggest a direct involvement of actin-myosin complexes in regulating transcription. It also implicates that actin and NMⅠ may co-exist in a same complex with RNAP Ⅱ and the interaction of RNAP Ⅱ with actin and NM Ⅰ functions in the RNAP Ⅱ-mediated transcription.