TABLE 2.

Summary of the catalytic activities of Flp, Flp(R191A), and Flp(R308A) on MeP substrates

The type I and type II endonuclease, strand joining, and strand exchange activities were assayed on MeP half-sites and are presented as percentages of the input substrate converted to product. The hydrolysis assays with Flp, Flp(R191A), and Flp(R308A) measured the sum of the type I plus type II endonuclease activities. The type II activities alone of the aforementioned proteins were deduced using their derivatives harboring the additional mutation Y343G. This mutation blocks the formation of the covalent tyrosyl adduct, which is the target for the type I endonuclease activity. Flp(R308A) was distinct in showing almost exclusively type II activity (Ref. 11 and this study). The extent of type I activity was estimated by subtracting the type II activity from total hydrolysis activity (type I plus type II). In the recombination reactions, strand exchange between a MeP half-site and a P full-site was assayed. ND, not determined.

	Hydrolysis of MeP-tyrosyl adduct (type I endonuclease)	Hydrolysis of MeP diester bond in DNA (type II endonuclease)	Strand joining in MeP half-site	Strand exchange between MeP half-site and P full-site
	%	%	%	%
Flp	2a	8	<1	0
Flp(R191A)	9	5	10	1
Flp(R308A)	<1	32a	<1	ND

^a Values taken from Ma et al. (11).