CLONING AND CHARACTERIZATION OF THE 5'-END AND PROMOTER REGION OF THECHICKEN ACETYL-COA CARBOXYLASE GENE

Acetyl-CoA carboxylase is a rate-limiting enzyme in the bios genesis o f long-chain fatty acids. In the present study, the 5' end and flankin g region of the acetyl-CoA carboxylase (ACC) gene was analysed in the chicken. A genomic clone was isolated containing the first three exons , the third one containing the ATG codon. Using nuclease-mapping exper iments and primer-extension analyses, the transcription-initiation sit e was located 153 nucleotides upstream of the ATG codon. In contrast w ith rat ACC gene expression, reverse transcriptase PCR analysis perfor med on chicken liver mRNA did not reveal alternative splicing in the 5 '-untranslated region of these messengers. The promoter region is very G+C rich, and contains no TATA or CAAT boxes. Analysis by transient t ransfection in a human hepatoma cell line (HepG2) demonstrates that th e promoter activity requires the presence of symmetrical sequences loc ated upstream of the GC boxes. Transcription of this gene is found to be controlled by tri-iodothyronine in HepG2 cells, but the sequence re sponsible for the tri-iodothyronine response is not the consensus trii odothyronine-responsive element localized in the promoter. These resul ts bring new insights to the regulation of the chicken ACC gene, which differs from that of the rat.