Nuclear actin and myosin I are required for RNA polymerase I transcription.

Authors :: Philimonenko VV
Zhao J
Iben S
Dingová H
Kyselá K
Kahle M
Zentgraf H
Hofmann WA
de Lanerolle P
Hozák P
Grummt I
Source :: Nature cell biology [Nat Cell Biol] 2004 Dec; Vol. 6 (12), pp. 1165-72. Date of Electronic Publication: 2004 Nov 21.
Publication Year :: 2004
Abstract: The presence of actin and nuclear myosin I (NMI) in the nucleus suggests a role for these motor proteins in nuclear functions. We have investigated the role of actin and nuclear myosin I (NMI) in the transcription of ribosomal RNA genes (rDNA). Both proteins are associated with rDNA and are required for RNA polymerase I (Pol I) transcription. Microinjection of antibodies against actin or NMI, as well as short interfering RNA-mediated depletion of NMI, decreased Pol I transcription in vivo, whereas overexpression of NMI augmented pre-rRNA synthesis. In vitro, recombinant NMI activated Pol I transcription, and antibodies to NMI or actin inhibited Pol I transcription both on naked DNA and pre-assembled chromatin templates. Whereas actin associated with Pol I, NMI bound to Pol I through the transcription-initiation factor TIF-IA. The association with Pol I requires phosphorylation of TIF-IA at Ser 649 by RSK kinase, indicating a role for NMI in the growth-dependent regulation of rRNA synthesis.