Lys-tRNA4 and cell division : Changes in lys-tRNA during the growth of mouse L cells

The presence of one isoaccepting tRNA species, lys-tRNA₄, has been correlated with the ability of mammalian cells to carry out cell division. The levels of this tRNA were measured during the growth of mouse L cells in culture. RPC-5 profiles of the lys-tRNA population of mouse L cells were determined at 9 points during the growth of mouse L cells in culture. The level of lys-tRNA₄ was constant at 13–14% of the total lys-tRNA population during log growth, increased to 18% when the cells became confluent and then returned to 13–14% when the cells were held at confluency. These results are in contrast to other cell lines where lys-tRNA₄ decreased at confluency. Confluent cultures of mouse L cells retained full proliferative potential since the addition of medium containing 30% serum led to renewed exponential growth. Another lys-tRNA species, lys-tRNA_5A, was present in variable amounts depending upon the nutritive state of the cells. The appearance of lys-tRNA_5A correlated with a decrease in lys-tRNA₅. These data suggest that lys-tRNA_5A is a modified lys-tRNA₅ which appears when the medium becomes depleted.