Structure and organization of the gene encoding rat S‐adenosylmethionine decarboxylase

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Abstract
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/intronjunctions 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 SI 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 I. Southern blot analyses reveal a complex hybridization pattern suggesting that there are multiple copies of the AdoMetDC gene in the rat genome.