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. 1998 Jul 1;12(13):1998–2012. doi: 10.1101/gad.12.13.1998

Figure 1.

Figure 1

Figure 1

 Procedure for randomization and selection of ESEs. (A) The natural ESE in mouse IgM exon M2 was replaced by a 20-nucleotide segment of random sequence, and a library of pre-mRNAs was constructed by overlap–extension PCR and in vitro transcription. A sample of this pool, representing ∼1.2 × 1010 pre-mRNA molecules was then spliced in vitro by complementation of an S100 extract with individual recombinant SR proteins. The pool of spliced mRNA products was gel purified, and the sequences corresponding to the ESE region were rebuilt into pre-mRNA template molecules for a new round of selection, or subcloned and sequenced. The sequences were analyzed by a motif-search algorithm to identify common patterns. (B) Sequence of the M2 exon of the mouse IgM gene. The sequence of the previously mapped ESE is shown in uppercase.