Table 1.

Activity, kinetic, and stability characteristics of archaeal ATases

Strain	Molecules per cell	Specific activity, fmol/mg protein	Kinetics, fmol/min*				Stability†t½, hr
			37°C	60°C	72°C	80°C	37°C	60°C	80°C
S. acidocaldarius	6,700	720	1.2	3.3	ND	11.4	32	16	0.5
Pyrococcus furiosus	1,100	85	ND	8.2	9.3	11.2	60	40	5
P. islandicum	66,700	4,280	ND	1.2	1.8	2.3	38	12	5.5
T. litoralis	10,800	380	ND	1.5	2.2	2.9	72	18	13

^*Initial rates of transfer of [³H]methyl groups from substrate DNA to protein in vitro. ND, not determined. 

^†Protein-limiting amounts of cell extracts were preincubated in IBSA at the temperatures indicated. Residual ATase activity was determined after addition of ³H-labeled substrate DNA and incubation at 75°C for 15 min. See text for details.