CHANGES OF THE PHOSPHORYLATION OF MEMBRANE-ASSOCIATED PROTEINS FOLLOWING TREATMENT OF HELA-CELLS WITH THE GUANINE ANALOG, QUEUINE

The guanine analogue, queuine (q), is a nutrition factor for eukaryote s and occurs as a free base or as modified nucleoside queuosine (Q) in serted into the anticodon of tRNAs(GUN) in place of guanosine (G). The free q-base and the corresponding Q-deficient tRNAs accumulate in fas t proliferating tumors and in embryonic cells. The present data show t hat treatment of Q-deficient HeLa cells with queuine resulted in reduc ed in vitro phosphorylation of two membrane-associated proteins, pp110 and pp18. Reduced phosphorylation of pp110 and pp18 was also observed when a membrane-containing particulate fraction from queuine starved HeLa cells was labelled with [gamma-P-32]ATP in the presence of queuin e. Incorporated phosphate into pp110 was alkali-stable, suggesting tha t this protein became phosphorylated at tyrosine residues. After stimu lation of intact Q-deficient cells with epidermal growth factor, pp110 was rapidly phosphorylated at tyrosine residues. The results show tha t queuine as a free base influences protein tyrosine phosphorylation i n intact cells, suggesting that it might interfere with protein phosph orylation involved in signal transduction pathways.