Sequence divergence of 5' extremities in rat liver alkaline phosphatase mRNAs

Structural analysis of 55 nearly full-length cDNA clones of rat liver alkaline phosphatase mRNAs revealed the presence of two totally different sequence stretches at the 5'-distal region starting from the position 88 nucleotides upstream of the initiation codon ATG. Since each of these two sequences, E1 and E2, was assigned on the rat genome about 36 kilobase pairs (kbp) and 10 kbp upstream of the common exon E3, respectively, they are presumably used as alternatively spliced exons. The distances between these sequences and E3 were unusually long, as compared with other intronic distances (0.4-4 kbp) observed between successive pairs of the eleven exons which are common to both types of mRNAs. The relative ratio of E1-containing mRNA to E2-mRNA was about three in the liver after bile-duct ligation and colchicine treatment.