Jh. Lee et al., REGULATION OF XENOPUS-LAEVIS ESTROGEN-RECEPTOR GENE-EXPRESSION IS MEDIATED BY AN ESTROGEN RESPONSE ELEMENT IN THE PROTEIN-CODING REGION, DNA and cell biology, 14(5), 1995, pp. 419-430
To investigate the 17 beta-estradiol induction of the mRNA coding for
the Xenopus laevis estrogen receptor (XER), we cloned the promoter and
the 5'-flanking region of the ER gene. Transcription initiation sites
were identified by primer extension, and confirmed by the polymerase
chain reaction. The promoter and 5'-flanking region contain an imperfe
ct TATA box and a potential CAAT box at -51. Sequence analysis and tra
nsfections indicated that no functional estrogen response element (ERE
) was present in approximately 3 kb of 5'-flanking region. An imperfec
t ERE, GGTCAGTTTGACG, which differs from the consensus ERE sequence by
1 nucleotide, was detected in the protein coding region of the gene,
approximately 480 nucleotides downstream of the transcription initiati
on site. In transient transfections using a simple promoter containing
two copies of this Xenopus estrogen receptor ERE (XERE), we observed
an estrogen-dependent increase in CAT activity of four- to five-fold,
to a level approximately 20-fold greater than the activity of the cont
rol plasmid lacking the XEREs. In competition gel mobility-shift assay
s, the XERE exhibited a weak, but clearly detectable, ability to compe
te for binding of human ER to a labeled consensus ERE. Because it exhi
bits sequence-specific binding to the ER in competition gel mobility-s
hift assays, and is able to confer estrogen-dependent transcription on
a simple synthetic promoter, the novel XERE, located in the protein c
oding region of the XER gene appears to represent a weak, but function
al, ERE.