THE PHOSPHORYLATION STATE OF PROTEASOMES AND α-RNP FROM RAT LIVER CELLS
A. S. Tsimokha, Yu. Ya. Vatazhok, E. S. Vashukova, V. A. Kulichkova, I. V. Volkova.
Yu. B. Ermolaeva, A. G. Mittenberg, I. N. Evteeva, V. A. Ivanov, L. N. Cause, I. M. Konstantinova
Institute of Cytology, RAS, St. Petersburg, Russia;
e-mail: atsimokha@mail.cytspb.rssi.ru
In eukaryotic cells the population of proteasomes is heterogeneous. Here we have shown that proteasomes from
nuclei and cytoplasm of rat liver cells differ in their subunit patterns. The subunit pattern of α-RNP differs from that
of proteasomes, however, α-RNP particles contain the number of 26S proteasome subunits. Moreover, the proteasomes contain
subunits of α-RNP. We have shown for the first time that nuclear proteasomes and a-RNP are hyperphosphorylated on
threonine residues. Differences in phosphorylation state of subunits of nuclear and cytoplasmic proteasomes and α-RNP on
threonine and tyrosine residues have been revealed. A suggestion is put forward that hyperphosphorylation of subunits may
determine nuclear localization of these complexes in rat liver cells. The results obtained suggest that a highly specialized
system of protein kinases and phosphatases may be involved in the regulation of phosphorylation state of different populations
of proteasomes and a-RNP in rat liver cells.
Key words: phosphorylation, proteasomes, α-RNP, threonine, tyrosine
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