Table I. Splicing efficiency of various reporters in msl5 mutant and wild-type strains.

Strain	msl5-2					msl5-3					msl5-9					MSL5-WT
reporter	WT	5′	BP	5′ + BP	–	WT	5′	BP	5′ + BP	–	WT	5′	BP	5′ + BP	–	WT	5′	BP	5′+ BP	–
m/p	11	0.4	3.2	0.3	–	24	0.4	4.6	0.3	–	23	1.1	4.1	0.02	–	34	5.8	15	1.6	–

Reporters contained the RP51A intron in the wild-type form (WT), with a mutation in the 5′ splice site (5′), in the branchpoint region (BP) or in both (5′ + BP). As a control for background from endogenous RNA, cells containing an empty vector (–) were analyzed. The signals corresponding to pre-mRNA and mRNA after primer extension were quantified and the ratio of mRNA/pre-mRNA (m/p) was calculated (Pikielny and Rosbash, 1985).