Functionally distinct isoforms of the CRE-BP DNA-binding protein mediate activity of a T-cell-specific enhancer.
Expression of the CD3 delta gene of the T-cell receptor (TCR) complex is regulated by a T-cell-specific enhancer. A highly conserved 40-bp motif (element delta A) within the CD3 delta enhancer is responsible for mediating its activity and specificity. Element delta A exhibits sequence similarities to the cyclic AMP response element (CRE) but does not respond to changes in the level of cyclic AMP. Using the delta A element as a probe, we have isolated three cDNA clones encoding three distinct protein isoforms, products of differential splicing and alternate promoter usage of the CRE-BP gene. These isoforms share the DNA binding and dimerization domains at the C terminus of the protein but differ at their N termini. In transfection assays, their activities as transcription regulators differ: CRE-BP2 is a potent activator, CRE-BP3 is a weak activator, and CRE-BP1 is transcriptionally inert. Mutations in the basic region of the CRE-BP1 protein which abrogate its ability to bind DNA render this protein a dominant repressor of the delta A enhancer. Antibodies to the CRE-BP protein interact specifically with the ubiquitous and predominantly T-cell-restricted nuclear complexes that bind to the delta A element and suggest the presence of this protein in homo- and heterodimeric complexes. Since the delta A motif is also present in the enhancer and promoter of the TCR alpha and beta genes, the CRE-BP isoforms may mediate expression of other members of the CD3/TCR complex during T-cell development.
Georgopoulos
K
K
Department of Molecular Biology, Massachusetts General Hospital, Boston 02114.
Morgan
B A
BA
Moore
D D
DD
D051698:Activating Transcription Factor 2; D000595:Amino Acid Sequence; D000818:Animals; D000945:Antigens, Differentiation, T-Lymphocyte / Q000235:genetics*; D001483:Base Sequence; D015152:Blotting, Northern; D017252:CD3 Complex; D002460:Cell Line; D003001:Cloning, Molecular; D017362:Cyclic AMP Response Element-Binding Protein; D004268:DNA-Binding Proteins / Q000235:genetics*; D004742:Enhancer Elements, Genetic / Q000235:genetics*; D016350:Leucine Zippers / Q000235:genetics; D046911:Macromolecular Substances; D051379:Mice; D008969:Molecular Sequence Data; D016296:Mutagenesis; D016133:Polymerase Chain Reaction; D011401:Promoter Regions, Genetic / Q000235:genetics; D011948:Receptors, Antigen, T-Cell / Q000235:genetics*; D013601:T-Lymphocytes / Q000378:metabolism; D014157:Transcription Factors / Q000235:genetics*
D051698:Activating Transcription Factor 2; D000945:Antigens, Differentiation, T-Lymphocyte; C497106:Atf2 protein, mouse; D017252:CD3 Complex; D017362:Cyclic AMP Response Element-Binding Protein; D004268:DNA-Binding Proteins; D046911:Macromolecular Substances; D011948:Receptors, Antigen, T-Cell; D014157:Transcription Factors