Fig. 5.

Alternative splicing for Abcg8 results from a CAG repeat at splice-acceptor boundary region in intron 1. Two sets of cDNAs were identified from the library screening that differed in the presence or absence of a CAG triplet codon at the boundary of exon 1 and exon 2 in the cDNA (A, electropherograms). Examination of the exon-intron boundary suggested that two possible choices for splice-acceptor sites existed (B, underlined). To confirm that alternatively spliced forms of Abcg8 were present in RNA isolated from normal mouse liver, jejunum, ileum, or colon, we exploited the loss of EcoO19I recognition sequence, if the CAG was deleted. Labeled PCR products (see Materials and Methods) were digested and separated by acrylamide gel electrophoresis (C). Although a PCR product size of 325 or 322 bp was expected, two other slower bands were identified, resulting from heteroduplexes formation (confirmed by direct sequencing of these bands). About 40% of the mRNA utilized the first CAG for splice-site identification and 60% utilized the next CAG (underlined). No significant differences between the various tissues in RNA alternative splice forms was detected.