Changes in Amount of Hypo‐Modified tRNA Having Guanine in Place of Queuine during Erythroid Differentiation of Murine Erythroleukemia Cells

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Abstract
The amounts of hypo-modified tRNAs having guanine in place of queuine in murine erythroleukemic cells decreased markedly when the cells differentiated into mature erythroid cells. The amounts of these hypo-modified tRNAs can be determined easily by measuring incorporation of labeled guanine into tRNA with Escherichia coli tRNA-guanine transglycosylase. The decrease was detected at on early stage of erythroid differentiation: namely, before any detectable increase in the percentage of cells containing hemoglobin. The amount of guanine-accepting tRNA species was nearly proportional to the percentage of undifferentiated cells in the population, regardless of the type of inducer used. Decrease in the amounts of hypo-modified tRNAs in the cells was effectively blocked by 12-O-tetradecartoylphorbol 13-acetate, which inhibits differentiation of these cells. 8-Azaguanine, which is known to be substrate of tRNA—guanine transglycosylase. was incorporated almost exclusively into the first position of hypo-modified tRNA in murine erythroleukemic cells when they were pulselabeled in culture with 8-azaguanine, suggesting strongly that tRNA-guanine transglycosylase in the cells is actually involved in incorporation of 8-azaguanine into tRNA in vivo. The amount of 8-azaguanine incorporated into tRNA in differentiated cells was one third of that in undifferentiated cells, the decrease being parallel with that in the amount of guanine-accepting tRNA in these cells. The results suggest that the appearance of hypomodified tRNAs in the transformed cells was due to lack of substrate for queuosine biosynthesis in tRNA.