Competence and progression growth factors stimulate different tRNAlys modification reactions in BALB/C 3T3 cells

Sparse cultures of Balb/C 3T3 cells were growth arrested in a medium containing 1% calf plasma. This treatment caused a decrease in tRNA4lys, a tRNA species related to cell division, and a corresponding increase in tRNA5lys. A restoration of tRNA4lys levels and an increase in cell number was obtained by the addition of either 10% calf serum or a combination of fibroblast growth factor and melanocyte stimulating activity. Neither growth factor alone evoked a proliferative response. The progression factors, insulin and multiplication stimulating activity stimulated the rapid conversion of tRNA5lys to tRNA2lys, whereas the competence factors, fibroblast growth factor and platelet-derived growth factor stimulated a slight conversion of tRNA2lys to tRNA4lys.