CORRECT USAGE OF MULTIPLE TRANSCRIPTION INITIATION SITES AND C EBP-DEPENDENT TRANSCRIPTION ACTIVATION OF THE RAT XDH/XO TATA-LESS PROMOTER REQUIRES DOWNSTREAM ELEMENTS LOCATED IN THE CODING REGION OF THE GENE/
Mp. Clark et al., CORRECT USAGE OF MULTIPLE TRANSCRIPTION INITIATION SITES AND C EBP-DEPENDENT TRANSCRIPTION ACTIVATION OF THE RAT XDH/XO TATA-LESS PROMOTER REQUIRES DOWNSTREAM ELEMENTS LOCATED IN THE CODING REGION OF THE GENE/, Nucleic acids research, 26(7), 1998, pp. 1801-1806
In the present study, we have shown that a downstream element located
in the coding region of the TATA-less rat xanthine dehydrogenase/oxida
se (XDH/XO) gene (-7 to +42) plays an important role in transcription
initiation and C/EBP transcriptional activation. Previous work from ou
r laboratory has shown that the promoter is organized with multiple in
itiator elements (Inr 1, 2, 3 and 4) which are important for transcrip
tion initiation. Additionally, we had identified two C/EBP binding sit
es upstream of this promoter. Deletional and mutational studies reveal
ed that C/EBP binding was not essential for the basal level of transcr
iptional initation. However when XO-luciferase constructs include down
stream sequence extending to +42 there is development of C/EBP sensiti
vity as well as a shift in the initiator usage. In the absence of the
downstream element, primer extension analyses reveals Inr 3 and 4 to b
e the major start sites but in the presence of this additional sequenc
e the usage is shifted to Inr 1 and 2, This shift in Inr usage more cl
osely resembles that seen in intact macrophages or liver cells. Gel mo
bility shift assays indicate the presence of several binding factors l
ocated in this downstream region, one of which has been identified as
YY-1, We postulate that YY-1 allows DNA bending which permits the upst
ream C/EBP elements to exhibit a transcriptional activation which is n
ot seen when the downstream element is absent. This study presents a p
otential model for regulation of the XDH/XO promoter.