Demonstration of promoter activity and alternative splicing in the region 5' to exon 1 of the APC gene.
Screening of fetal brain and fetal retina complementary DNA (cDNA) libraries and exon-connection experiments using brain cDNA have identified three exons 5' to exon 1 of the adenomatous polyposis coli gene. The exons are termed (from 5'-3') 0.3, 0.1, and 0.2; exons 0.1 and 0.2 are contiguous genomically. Library screening revealed alternatively spliced cDNAs containing the following combinations of 5'-exons: 0.3 + 1 + 2, 0.3 + 2, 0.1 + 0.2 + 1 + 2, and 0.1 + 1 + 2. Exon-connection experiments also identified these four forms in mRNAs from tissues and cultured cell lines, along with two additional forms, 0.1 + 0.2 + 2 and 0.1 + 2. The multiple splice forms may lead to proteins of differing activity; for example, products derived from cDNAs without exon 1 will lack most of a heptad-repeat domain that supports formation of homodimers. No mRNA species combining 0.3 with either 0.1 or 0.2 were identified. The existence of two apparently separate 5'-ends of APC suggests the possibility of two independent promoters. The genomic sequence adjacent to exon 0.3 confers promotor activity when cloned in a chloramphenicol acetyltransferase expression vector and transfected into a colon cancer cell line.
Thliveris
A
A
School of Medicine, University of Utah, Salt Lake City 84112.
Samowitz
W
W
Matsunami
N
N
Groden
J
J
White
R
R
D017398:Alternative Splicing / Q000235:genetics*; D000595:Amino Acid Sequence; D001483:Base Sequence; D015500:Chloramphenicol O-Acetyltransferase / Q000235:genetics; D018076:DNA, Complementary / Q000235:genetics; D005091:Exons / Q000235:genetics*; D017491:Genes, APC / Q000235:genetics*; D006801:Humans; D008969:Molecular Sequence Data; D011401:Promoter Regions, Genetic / Q000235:genetics*; D012333:RNA, Messenger / Q000235:genetics
D018076:DNA, Complementary; D012333:RNA, Messenger; D015500:Chloramphenicol O-Acetyltransferase