Figure 2.

In vitro transcription and translation of constructs containing alternative upstream exons joined to CFTR exons 2–24. (A and B) In vitro transcription and translation. ³⁵S-labeled proteins separated by SDS-PAGE and visualized by autoradiography. The products from full-length CFTR (936C) and exons 2–24 are marked by arrows (A and B, respectively). (A) Inclusion of exon −1a in the transcript generates the same products as exons 2–24 alone, whereas inclusion of exons −1a/1a together inhibits translation. (B) Mutation of the potential CTG and ATG initiation codons in exon 1a does not restore translation from more distal ATGs in exon 4. (C) In vitro transcription. RNA transcripts were generated with T7 polymerase, denatured after RNase-free DNase treatment, and separated on a formaldehyde agarose gel, poststained by ethidium bromide. Stable RNA was generated from all constructs. (D) Partial sequence of exon 1a and location of potential initiation sites. The CTG and ATG potential initiation sites are in italics, and the mutations in capitals.