Trends in Biochemical Sciences
Role of the CCAAT-binding protein CBF/NF-Y in transcription
Section snippets
The CCAAT motif is a functional promoter element
Generally, mutations in the CCAAT motif cause a several-fold decrease in transcription activity both in vitro and in vivo3, 4, 5, 6. Table 1 shows examples of different mammalian promoters, which have been divided into three groups based on the effect of a CCAAT motif mutation on promoter activity. Mutations in the CCAAT motifs of group 1 promoters result in decreased transcription in the absence of stimulatory influences4, 5, 6, 7, 8, 9, 10. In promoters of group 2, similar mutations alter
CBF/NF-Y binds specifically to the CCAAT motif
To date, several proteins have been isolated that bind to CCAAT motifs; among these, CBF/NF-Y (also called CP1; referred to herein as CBF; see Appendix A) requires a high degree of conservation of the CCAAT sequence. Indeed, nucleotide-substitution mutations in each base of the CCAAT motif result in either loss or decrease in formation of the CBF–DNA complex. Other CCAAT-binding proteins include CTF/NF1 and CCAAT/enhancer-binding protein (C/EBP), but DNA sequences in the binding sites of these
Subunit assembly and DNA binding
Recombinant CBF polypeptides have been used to demonstrate that CBF-A and CBF-C interact with each other to form a stable heterodimer. CBF-B only interacts with the CBF-A/CBF-C heterodimer, not with CBF-A or CBF-C alone, to form a heterotrimeric CBF molecule, which then binds to DNA. The conserved segments of CBF-A and CBF-C that are necessary for formation of a CBF–DNA complex show amino acid sequence homology with each other. Interestingly, these two CBF segments display amino acid sequence
The flanking sequences of the CCAAT motif as determinants of CBF-binding affinity
Analysis of the CBF-binding sites indicates that mutations of each nucleotide of the CCAAT sequence in promoters decreases or abolishes CBF binding. Also, not all promoter DNAs containing the CCAAT sequence bind CBF, suggesting that specific nucleotide sequences other than CCAAT are necessary for CBF binding. Specific DNA sequences that are required for CBF binding have been defined by using PCR-mediated random binding selection[33]. This experiment indicated that the affinity of CBF binding to
Two separate transcriptional activation domains
Transcription of the α2(1) collagen promoter and of the Rous sarcoma virus long terminal repeat (RSV-LTR) is stimulated severalfold by the addition of purified recombinant CBF subunits to mouse nuclear extracts that were previously depleted of CBF. Analysis of CBF deletion mutants in such an in vitro transcription system identified two transcription activation domains in the heterotrimeric CBF, one present in CBF-B, the other in CBF-C, which activate transcription additively. The two CBF
Transcriptional regulation of different mammalian promoters by CBF
One way that CBF might regulate the transcription of various promoters is by cooperative interactions with other transcription factors that bind to a specific promoter. The liver-specific serum albumin promoter contains a CBF-binding site that is juxtaposed to a strong binding site for the C/EBP transcription factor. C/EBP and CBF activate transcription synergistically in liver nuclear extracts in vitro. However, this transcriptional synergism is not observed when the CBF binding site is moved
Concluding remarks and perspectives
CBF is a unique DNA-binding protein that interacts with the CCAAT motif, a common element present in various mammalian promoters. Portions of each of the three CBF subunits that are needed for DNA binding are conserved from yeast to human. The CCAAT motif is present in a limited number of yeast promoters and the CBF homolog in yeast regulates the transcription of nuclear genes that are involved in mitochondrial function. The conserved segments of two CBF subunits show homology with the ancient
Acknowledgements
Work performed in the laboratories of the authors was supported by grants from the National Institutes of Health.
References (39)
J. Mol. Biol.
(1990)- et al.
Cell
(1988) Cell
(1987)- et al.
J. Biol. Chem.
(1993) - et al.
J. Biol. Chem.
(1993) - et al.
J. Biol. Chem.
(1996) - et al.
J. Biol. Chem.
(1995) - et al.
J. Biol. Chem.
(1996) - et al.
J. Biol. Chem.
(1996) - et al.
J. Biol. Chem.
(1996)
J. Biol. Chem.
J. Biol. Chem.
Trends Genet.
Methods Enzymol.
J. Biol. Chem.
J. Biol. Chem.
J. Biol. Chem.
J. Biol. Chem.
Science
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