DYNAMIC PHOSPHORYLATION OF RNA POLYMERASE III HOLOENZYME SUBUNITS FROM HUMAN EPIDERMOID CARCINOMA CELLS A431
CULTIVATED UNDER DIFFERENT CONDITIONS
N. A. Merkulova, V. M. Sedova
Institute of Cytology RAS, St. Petersbrg;
e-mail: sedova@mail.cytspb.rssi.ru
Dynamic phosphorylation in vivo of individual subunits of holoenzyme RNA polymerase III subfractions IIIa
and III b on serine/threonine and tyrosine aminoacid residues has been shown in human epidermoid carcinoma cells
A431. Cells cultivation under starvation on embryonic serum caused a prolongation of the cell cycle, while
cultivation at low concentration of epidermal growth factor (EGF) activated cell proliferation. Subunit 45 kDa is
phosphorylated on serine/threonine residues in subfraction IIIa only in starving cells. This subunit of subfraction
IIIb is unphosphorylated. Phosphorylation of this particular subunit is restored under induction by EGF at low
concentration (0.1 ng/ml). The level of phosphorylation on tyrosine aminoacid residues of subunits of holoenzyme
subfractions IIIa and IIIb is high in cells cultivated under starvation. Subunit 60 kDa has a higher level of
phosphorylation as compared with subunits 45 and 38 kDa. Induction by EGF at low concentrations increases the level
of phosphorylation of subunits 60 and 38 kDa in both subfractions of holoenzyme.
Back
Contents
Main
