Possible involvement of queuine in control mechanisms of protein synthesis and protein phosphorylation in eukaryotes.

The functional role of the deazaguanine-derivative queuine was investigated using virus-transformed erythroleukaemic cells of mice as a model. The two-dimensional patterns of [35S]methionine-labelled proteins on two-dimensional O'Farrell gels of queuine-deficient (Q-), compared with queuine-supplemented (Q+) growing cells, showed specific characteristic alterations in the synthesis of 36 and 42 kd basic proteins. According to pI values and immunoreactivity with anti-LDH antibodies, the 36 kd proteins represent various forms of LDH A subunits or closely related proteins. Cell-free systems of protein synthesis were established from growing (Q-) or (Q+) cells. Addition of 3 x 10(-8) M queuine to the (Q-) in vitro system inhibited the incorporation of [35S]methionine into total protein to approximately 20%; raising the concentration of queuine up to 1 x 10(-6) M did not increase the inhibitory effect appreciably. In the (Q-) system, a series of 36 kd proteins, with pI values corresponding to LDH A isoforms, were synthesized. The in vitro synthesis of these proteins was completely inhibited by addition of queuine at a concentration of 3 x 10(-8) M. Furthermore, the expression of certain other proteins was lower in the (Q+) than in the (Q-) in vitro system. Labelling of growing (Q+) or (Q-) cells with [32P]orthophosphate and subsequent analysis of phosphoproteins on two-dimensional O'Farrell gels showed that queuine inhibited the synthesis of distinct phosphoproteins. Protein synthesis performed in cell-free (Q-) or (Q+) systems in the presence of non-labelled amino acids and 32P-labelled gamma ATP also indicated that queuine interferes with the synthesis and/or phosphorylation of particular phosphoproteins.