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Fig. 2. Differential splicing of exon 9a. A, diagrammatic illustration of the differential splicing event resulting in the inclusion of exon 9a. The additional 42 nucleotides and 14 amino acids included as a result of this event are indicated in uppercase and bold, respectively. The location of primers used for PCR (A and B) and for sequencing (C and D) are indicated by arrows. B, RT-PCR analysis of adult mouse tissue RNAs, E10.5 embryo RNA, and cell line RNA. RNA was reverse transcribed with random primers and then PCR amplified with primers A and B (top panel). Amplification of the 796-bp fragment is indicative of the KSR1 isoform, whereas amplification of the 838-bp fragment is indicative of the B-KSR1 isoform containing exon 9a. As a control, the reverse-transcribed cDNAs were also amplified with primers for the raf-1 gene that generate a 357-bp product in all samples (bottom panel).