Table 3. Homologous recombination frequency (HRFb) in wt CBS7435 and ku70 deletion strains.

Recipientstrain	Locus	Length of homology on each side	Auxotrophic/total number of transformants counted	HRFb%
wt	HIS4	∼1350 bp	44/266	16.5
		∼1000 bp	31/268	11.6
		∼650 bp	32/268	11.9
		∼250 bp	8/268	3.0
		∼100 bp	1/268	0
	ADE1	∼650 bp	0/>103	0
		∼400 bp	0/>103	0
		∼150 bp	11/>103	0
		∼50 bp	0/>103	0
ku70	HIS4	∼1350 bp	267/268	100
		∼1000 bp	268/268	100
		∼650 bp	267/268	100
		∼250 bp	86/89	96.6
		∼100 bp	20/57	35.1
	ADE1	∼650 bp	465/533	87.9
		∼400 bp	114/172	75.4
		∼150 bp	12/99	17.5
		∼50 bp	1/317	0

Over 95% homologous recombination frequencies could be reached in the ku70 deletion strain with as little as 250 bp of homologous sequence on each side of the integration cassette. In the corresponding wild-type strain, only 16.5% homologous recombination frequency was reached with the longest (1350 bp) homologous sequence tested.