The independent regulation of tRNA(iMet) and tRNA(Asn) synthesis during Friend cell erythroid differentiation

In this report, we have compared the changes in the production of tRNA(iMet) (initiator tRNA(Met] and tRNA(Asn), which occur during erythroid differentiation in the Friend erythroleukemia cell. The relative steady-state concentration of these two tRNAs (relative to the total tRNA population) was measured by aminoacylation. The results show that while the relative steady-state concentration of tRNA(iMet) changes very little in the cytoplasmic tRNA population, the relative concentration of tRNA(Asn) decreases during the first two days of differentiation and then undergoes an increase. This difference in the behavior of these two tRNAs is also seen when their relative concentrations in newly synthesized tRNA is examined. When tRNA is labeled with tritiated uridine for 24 h in vivo prior to isolation, the hybridization of this labeled tRNA to filter-bound tRNA genes shows that the relative concentration of tRNA(iMet) in newly synthesized tRNA changes very little, while the relative concentration of newly synthesized tRNA(Asn) again decreases through the first 2 days of differentiation, and then undergoes a smaller increase. Thus, the production of these two tRNAs appears to be independently regulated. Independent regulation of synthesis is also observed when examining the production of these two tRNAs in isolated nuclei. During erythroid differentiation, the relative synthesis of tRNA(iMet) (relative to total nuclear RNA synthesis) remains constant, while the relative synthesis of tRNA(Asn) undergoes periodic increases and decreases in value.