Table 4.

Effects of siRNA knockdown of Polλ on mutation frequencies and nucleotides inserted opposite a cis-syn TT dimer or a (6-4) TT photoproduct carried on the leading or lagging strand DNA template in nucleotide excision repair–defective XPA human fibroblasts.

DNA lesion	Lesion containing DNA strand	siRNA	Nucleotide inserted						Mutation frequency %
			# of Kan+ blue colonies sequenced	A	G	C	T	Othera
cis-syn TT dimer	Leading	NC	334 (7)b	327	4 (3′ T)c	—	2 (5′ T)	–	2.1
							1 (3′ T)
		Polλ	402 (3)	399	3 (3′ T)	—	—	—	0.7
	Lagging	NC	375 (10)	365	4 (5′ T)	—	1 (5′ T)	—	2.7
					2 (3′ T)		3 (3′ T)
		Polλ	318 (2)	316	2 (3′ T)	—	—	—	0.6
(6-4) TT photoproduct	Leading	NC	342 (8)	334	3 (5′ T)	—	2 (3′ T)	1	2.3
					2 (3′ T)
		Polλ	347 (15)	332	1 (5′ T)	6 (3′ T)	4 (3′ T)	2	4.3
					2 (3′ T)
	Lagging	NC	384 (7)	377	2 (5′ T)	—	2 (3′ T)	1	1.8
					2 (3′ T)
		Polλ	320 (16)	304	4 (5′ T)	4 (3′ T)	3 (3′ T)	2	5.0
					3 (3′ T)

^aMutations at the flanking site.

^bNumbers of colonies where TLS occurred by insertion of a nucleotide other than an A are shown in parenthesis.

^cThe site where mutation occurred, 3′T or 5′T of the UV lesion is indicated in parenthesis.