Structure and organization of the gene encoding rat S-adenosylmethionine decarboxylase.

The gene for S-adenosylmethionine decarboxylase (AdoMetDC) was isolated from a rat genomic library using AdoMetDC cDNA as a probe. Nucleotide sequence analysis shows that the rat AdoMetDC gene consists of 8 exons which encode a protein identical to that inferred by a rat AdoMetDC cDNA sequence. The exons range in length from 43 to 1964 base pairs spanning 15672 bases of chromosomal DNA. All of the exon/intron junctions were found to conform to the consensus splice donor and acceptor sequences. Exon 8 corresponds to the 3' noncoding region of the 2 species of AdoMetDC mRNA which are formed by alternative utilization of 2 polyadenylation signals separated from each other by 1272 nucleotides. The transcription initiation site was located by S1 nuclease protection and by primer extension analysis, -325 nucleotides upstream of the translation initiation codon. The promoter region of the rat AdoMetDC gene contains a TATA box at -29 base pairs. No typical GC or CAAT boxes are located in the promoter, but six GC boxes and several putative binding sites for both tissue-specific and non-specific transcription factors are found in the proximal part of intron 1. Southern blot analyses reveal a complex hybridization pattern suggesting that there are multiple copies of the AdoMetDC gene in the rat genome.