Structure of the mouse Adh-1 gene and identification of a deletion in a long alternating purine-pyrimidine sequence in the first intron of strains expressing low alcohol dehydrogenase activity

Abstract

The ethanol-active alcohol dehydrogenase (ADH-A2) expressed at high levels in mouse liver is encoded by the Adh-1 gene. Inbred strains differ in the amount of ADH-A2 expressed. We report here the cloning and sequencing of the Adh-1 genes from mouse strains that express high and low amounts of ADH-A2 in liver (strains YBR/Ki and Balb/c respectively). The gene contains nine exons, and encodes an ADH-A subunit identical to that encoded by the cDNA isolated from DBA/2J, a strain with low liver ADH activity. This demonstrates that the difference between strains in liver ADH activity is not due to differences in the amino acid sequence of the ADH-A2. The 5'-nontranslated region and at least the first 225 bp 5' to the transcriptional start point are identical in both strains. We have found restriction fragment length polymorphisms in the Adh-1 gene that correlate with the level of expression of ADH-A2 in different strains. One of these RFLPs is within a remarkably long (288 bp) strictly alternating purine-pyrimidine sequence located in the first intron. This region in YBR/Ki contains 25 copies of the sequence ATGT(A/G)T (four of them inverted), which closely resembles important elements in the SV40 enhancer region. Balb/c mice, which express Adh-1 at lower levels, have a deletion that removes 101 bp of this sequence and also have several transition mutations; the comparable region has nine fewer ATGT(A/G)T repeats. These results suggest that the difference in gene expression may be due to differences in these hexamers or in other portions of the alternating purine-pyrimidine sequences, rather than in cis-acting sequences in the proximal 5' (promoter) region.