FIG. 3.

Characterization of an SC35-dependent splicing enhancer in exon 2. (A) The dsx[hβ 50-87] derivatives are overlapping subfragments of the full-length hβ-globin exon 2 fragment comprising nt 50 to 87 (see Fig. 1D and 2A for numbering system; see also Materials and Methods). The chimeras are indicated schematically and labeled similarly to those in Fig. 2A. Sequences of the β-globin exon subfragments are shown in capital letters and their relative positions within the dsx[hβ 50-87] fragment are indicated. Polylinker sequences contributed by the vector are indicated in lowercase letters. (B) The dsx[hβ 63-80] mutants are substitution mutants of the UGCUGUU sequence. Mutations within the putative degenerate heptameric SC35 consensus sequence are indicated by outlined letters. The chimeras are indicated schematically and labeled similarly to those in Fig. 3A. (C) S100 complementation assays with recombinant SC35 using dsx pre-mRNA substrates with various subfragments of β-globin exon 2 nt 50-87 fragment and mutants of the β-globin exon 2 nt 63-80 subfragment were subcloned 30 nt downstream of the dsx 3′ splice site. The figure is labeled similarly to Fig. 1.