appear that many, and perhaps all, genes contain multiple response elements 
such that the rate of expression of a given gene at any given point in time is 
dependent on the integrated effects of many transcription factors. 
Transcription factors contain a DNA-binding domain (e.g., zinc finger or 
homeodomain) that is rich in positively charged amino acids. Many 
transcription factors, such as the Fos/Jun family, also contain an additional 
structural motif (e.g., LZ) that enables them to dimerize and thereby form an 
active DNA-binding protein complex. In fact, different members of the Fos/Jun 
family have been shown to dimerize with each other, and such heterodimers 
TABLE 1 . Examples of transcription factors and their DNA-binding sites 
Transcription Factor 
Binding Site 
Response Element 
Structural Motif 
CREB family 
CRE 
TGACGTCA 
LZ 
Fos/Jun family 
AP-1 
TGACTCA 
LZ 
ZiU 268 
GC rich 
? 
ZF 
SP1 
GC box 
GGGCGG 
ZF 
Steroid receptor 
GRE 
GGTACANgTGTTCT 
ZF 
family (e.g., GR) 
POU family 
POU 
ATTTGCAT 
HD 
(e.g., OCT, Pit) 
AP-2 
AP-2 
CCCCAGGC 
? 
(protein unidentified) 
SRF 
SRE 
GATGTCCATA- 
TTAGGACATC 
? 
HSF 
HSE 
? 
? 
KEY: LZ=leucine zipper; ZF=zinc finger; HD=homeodomain; GR=glucocorticoid 
receptor; SRF=serum response factor; HSF=heat shock factor; GC=guanosine 
and cytosine; GRE=glucocorticoid response element; SRE=serum response 
element; HSE=heat shock response element 
SOURCE: Adapted from Mitchell and Tjian 1989; Goodman 1990; Morgan and Curran 
1991 
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