Abstract
Starvation inhibits and refeeding stimulates transcription of the malic enzyme gene in chick liver. DNA between -320 and +72 base pairs (bp) is DNase I-hypersensitive in hepatic nuclei from fed but not starved chicks (Ma, X. J., and Goodridge, A. G. (1992) Nucleic Acids Res. 20, 4997-5002). A polypyrimidine/polypurine (PPY/PPU) tract lies within the DNase I-hypersensitive region. In hepatocytes transiently transfected with plasmids containing triiodothyronine response elements and a minimal promoter from the malic enzyme gene linked to the chloramphenicol acetyltransferase gene, deletion of the PPY/PPU tract inhibited chloramphenicol acetyltransferase activity by about 90% with or without triiodothyronine. Fine mapping of S1 nuclease-sensitive sites suggests that the PPY/PPU tract can assume different isoforms of non-B-DNA, some of which may be triplex structures. The PPY/PPU tract contains specific binding sites for single- and double-stranded DNA binding proteins and, with 8 bp 3' of the tract, can function as a promoter. A (CT)7 repeat binds single-stranded DNA-binding protein and is essential for promoter activity. Two C-rich elements bind single-stranded DNA-binding proteins and may mediate inhibition of promoter function. The single- and double-stranded DNA-binding proteins that interact with the PPY/PPU tract may regulate transcription of the malic enzyme gene.
Highlights
Ers that lack TATA-box elements (4 –7)
We tested the functional significance of the PPY/PPU sequence in the malic enzyme promoter by comparing transcription from a promoter containing the wild-type sequence with that in a construct lacking all but 4 bp of the PPY/PPU tract. pBH147CAT contains a T3 response unit and a minimal promoter from the chicken malic enzyme gene linked to a chloramphenicol acetyltransferase (CAT) reporter gene (Fig. 1B)
In cells transfected with pBH147⌬PPYCAT, T3-induced expression of CAT was 80% less than that in cells transfected with pBH147CAT; the decrease was about 90% in cells not treated with T3
Summary
Ers that lack TATA-box elements (4 –7). These promoters are usually GC-rich, have multiple transcription start sites, and use initiator sequences to identify where the initiation complex should bind and initiate transcription. On the top DNA strand, S1 nuclease detected a major single-stranded region between Ϫ104 and Ϫ91 bp; this region of the PPY/PPU tract contains a (CT)7 repeat. We used another single-strand-specific endonuclease, P1 nuclease, to probe DNA structure in the region of the PPY/ PPU tract.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
