Table 1. Heterologous reconstitution of RNase P protein and RNA subunits at (A) 37°C and (B) 55°C.

Protein subunit	RNA subunit	nmol product/ nmol RNA (min)	% cleavage by homologous T.maritima complex
A
T.maritima	T.maritima	6.6 ± 0.6	100
T.maritima	E.coli	5.1 ± 1	77
T.maritima	T.thermophilus	2.2 ± 0.7	33
E.coli	T.maritima	6.1 ± 0.3	93
E.coli	E.coli	5.6 ± 1.4	85
E.coli	T.thermophilus	1.0 ± 0.4	15
B
T.maritima	T.maritima	6.5 ± 1.6	100
T.maritima	E.coli	3.8 ± 1.4	58
T.maritima	T.thermophilus	0.7 ± 0.04	11
E.coli	T.maritima	0	–
E.coli	E.coli	0	–
E.coli	T.thermophilus	0	–

The initial velocities of cleavage of precursor tRNA^Tyr were determined by incubation of 1 nM of the RNA subunit and 10 nM of the protein subunit in reaction buffer (400 mM NH₄Cl, 50 mM HEPES, pH 7.5, 5 mM MgCl₂) for 5 min at 50°C. The reactions were started by addition of 100 nM of ³²P-labeled substrate (see Materials and Methods). Aliquots were taken at 1 min intervals and separated on 8% polyacrylamide/7 M urea denaturing gels. The amount of cleavage was determined with a phosphoimager. A ‘homologous’ complex refers to a complex that contains protein and RNA subunits from the same organism.