Wilhelm bernhard workshop on the cell nucleus

ß-Actin, TAta binding protein (TBP) and transcription by RNA polymerase II (RNAPII)

de Lanerolle P., Mavrommatis E., Johnson, T., Hoffman W., Stojiljkovic L., Fuchsova B., Philimonenko V.¹ and Hozak P.¹

Department of Physiology, University of Illinois at Chicago, Chicago, USA and ¹Institute of Experimental Medicine, Academy of Sciences of the Czech Republic, Prague, Czech Republic

Actin is abundant in the nucleus and actin is reported to co-purify with RNAPII (Egly et al., 1984). We have also demonstrated that a new isoform of myosin I in the nucleus (Pestic-Dragovic et al., 2000). Nuclear myosin I (NMI) co-localizes with RNA polymerase II (RNAPII) and antibodies to NMI inhibit transcription by RNAPII. We now report that the microinjection of antibodies to NMI or to ß-actin into the nuclei of HeLa cells block transcription, in vivo. Assays using purified RNAPII, recombinant TBP, TFIIB and TFIIF and negatively supercoiled DNA showed that antibodies to NMI or to ß-actin inhibited transcription, in vitro, while control antibodies did not. We have also found ß-actin in pre-initiation complexes (PIC). Furthermore, TBP co-IP's with ß-actin and vice versa in the presence or absence of sarcosyl. Other experiments have shown that ß-actin co-localizes with TBP. Binding studies using peptides derived from ß-actin have shown that certain peptides inhibit the ß-actin-TBP interaction while other peptides do not. Based on these data, we propose ß-actin is involved in PIC formation through an interaction with TBP and that ß-actin and NMI act as molecular motors to power transcription by RNAPII.

References:

Egly et al., EMBO J. , 3: 2363-71, 1984

Pestic-Dragovic et al., 2000