TABLE 3.

Levels of RNase P RNA and amounts and rates of synthesis of tRNAs in the HeLa cell nucleocytoplasmic compartment and mitochondria, S. cerevisiae mitochondria, and E. coli

Cell	No. of tRNA molecules/cell	Rate of tRNA synthesis (molecules/min/cell)c	No. of RNase P molecules/cell	Ratio of RNase P molecules/cell to rate of tRNA synthesis
HeLa cells	7.7 × 107a	8.0 × 104	54.4 × 103d	0.678
Nucleocytoplasmic compartment
Mitochondria	6 × 105a	630	33–175d	0.052–0.28
S. cerevisiae mitochondria	5 × 104b	≈4 × 102	40b	0.11
E. coli	3 × 105a	104	500e	0.05

^aFrom reference 28. 

^bFrom reference 41. 

^cBased on a doubling time of 16 h for HeLa cells (29), 120 min for S. cerevisiae, and 30 min for E. coli. 

^dThis work. 

^eS. Altman, personal communication.