The structure of the gene for murine CTP:phosphocholine cytidylyltransferase, Ctpct. Relationship of exon structure to functional domains and identification of transcriptional start sites and potential upstream regulatory elements.
Phosphatidylcholine (PC) is the most abundant eukaryotic phospholipid and serves critical structural and cell-signaling functions. CTP:phosphocholine cytidylyltransferase (CT) is the rate-limiting enzyme in the CDP-choline pathway of PC biosynthesis, which is utilized by all tissues and is the sole or major PC biosynthetic pathway in all non-hepatic cells. Herein, we present the complete structure of the murine CT (Ctpct) gene. One P1 genomic clone and six subsequent plasmid subclones were isolated and analyzed for the exon-intron organization of the Ctpct gene. The gene spans approximately 26 kilobases and is composed of 9 exons and 8 introns. The exons match the distinct functional domains of the CT enzyme: exon 1 is untranslated; exon 2 codes for the nuclear localization signal domain; exons 4-7 encompass the catalytic domain; exon 8 codes for the alpha-helical membrane-binding domain; and exon 9 includes the C-terminal phosphorylation domain. Two transcriptional initiation sites, spaced 35 nucleotides apart, were identified using 5'-rapid amplification of cDNA ends polymerase chain reaction. The 5' natural flanking region was found to lack TATA or CAAT boxes and to contain GC-rich regions, which are features typical of promoters of housekeeping genes. Several sites that have the potential to interact with transcription regulatory factors, such as Sp1, AP1, AP2, AP3, Y1, and TFIIIA, were identified in the 5'-region of the gene and found to be distributed in two distinct clusters. These data will provide the basis for future studies on the cis- and trans-acting factors involved in Ctpct gene transcription and for the creation of induced mutant mouse models of altered CT activity.
Tang
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Department of Medicine, Columbia University College of Physicians and Surgeons, New York, New York 10032, USA.
Keesler
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GA
Tabas
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D000818:Animals; D001483:Base Sequence; D019916:Choline-Phosphate Cytidylyltransferase; D002874:Chromosome Mapping; D003001:Cloning, Molecular; D051379:Mice; D008969:Molecular Sequence Data; D009713:Nucleotidyltransferases / Q000235:genetics*; D017422:Sequence Analysis, DNA
D009713:Nucleotidyltransferases; D019916:Choline-Phosphate Cytidylyltransferase