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.