TABLE 1.

Purine- and pyrimidine-rich sequences in the selected splicing enhancers

Clone no.	Splicing enhancer sequencea	Splicing efficiencyb (%)
Class I, purine-rich enhancers (≥65% purine content)
Motif A, GGGGA
3-7	GCAACGGGGACGCGGC	40
3-1	AGCGGUCGCGGUUGGGGGag	32
6-43	GCGGAGGAGGCCCGUGGGag	50
Motif B, GGAGGA
6-43	GCGGAGGAGGCCCGUGGGag	50
6-19	GCCAGCGGAGGAUGCGG	53
Motif C, GGAGA
3-35	CUGGAAUACGGAGACCGG	36
6-40	GGUGAGCGGAGAUGCUGC	31
Others
3-36	GGACCUAGAGGUGGCGAC	40
6-29	GACCGUCGGACAGGAGC	36
Class II, pyrimidine-rich enhancers (≥67% pyrimidine content)
Motif D, UCUCC
6-13	auCUCCACGUCGCCUGCUGC	38
6-16	auCUCCACGUCGCCUGCUGC	37
6-24	UUUGCGGUCUCCGGCCUCC	56
Motif E, UCUUC
6-5	UGCCACCCGCGGUCUUCC	26
6-12	UCGUCGUCUUCGCGGCCC	49
3-32	CCUGCUGCGUCUUUGUCC	27
Motif F, UCCUC
6-7	CCUGUCCUCGGUGUUGC	36
6-22	CGUCCUCGUGUCACCGCC	37
6-6	GGUUCCUGUCGCCGCCCC	41
Controls (reference)
dsx, enhancerless		≤1
hβ-globin (51)		81
dsx-ASLV (60)		58

^aBoldface letters indicate purine- and pyrimidine-rich tracts consisting of five or more consecutive nucleotides; uppercase letters indicate splicing enhancer sequences specific to the indicated clone; lowercase letters indicate sequences common to all clones; underlining indicates the position of sequence deviation from the motif. The splicing enhancers are in the sequence context gcauNNNNNNNNNNNNNNNNNNaguc. Note that some of the enhancers contain 16, 17, or 19 nt. 

^bQuantitated as described in the legend to Fig. 2 according to formula [S][S + P]⁻¹ × 100, where S is the spliced product and P is the precursor RNA.