The B subunit of a rat heteromeric CCAAT-binding transcription factor shows a striking sequence identity with the yeast Hap2 transcription factor.
CBF is a heteromeric mammalian transcription factor that binds to CCAAT sequences in a number of promoters such as the two type I collagen promoters, the albumin promoter, the major histocompatibility complex class II promoter, and others. It is composed of two components, A and B, that are both needed for DNA binding. We have isolated a rat cDNA containing the complete 341-amino acid coding sequence of the B component of CBF. Expression of this cDNA in vitro generates a polypeptide that shows the same dependency on the A component as the native B component in the formation of a complex with a CCAAT-containing DNA. The C-terminal portion of the B component from residue 260 to residue 312 shows a 75% sequence identity with a portion of the Hap2 protein, a component of a heteromeric CCAAT-binding protein in yeast. In contrast, the rest of the protein shows little sequence homology with Hap2, although both proteins contain glutamine-rich domains. In the B component of CBF this domain spans the amino-terminal 60% of the protein, whereas in Hap2 this domain is much smaller. Hence, only a few changes in one domain of this protein were tolerated during evolution between yeast and mammals, whereas the rest of the protein diverged much more extensively.
Maity
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Department of Molecular Genetics, University of Texas, M. D. Anderson Cancer Center, Houston 77030.
Vuorio
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T
de Crombrugghe
B
B
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D023081:CCAAT-Binding Factor; D022762:CCAAT-Enhancer-Binding Proteins; D002467:Cell Nucleus / Q000378:metabolism; D002846:Chromatography, Affinity; D003001:Cloning, Molecular; D004268:DNA-Binding Proteins / Q000235:genetics* / Q000302:isolation & purification; D005656:Fungal Proteins / Q000235:genetics*; D008099:Liver / Q000378:metabolism; D046911:Macromolecular Substances; D008969:Molecular Sequence Data; D008970:Molecular Weight; D015345:Oligonucleotide Probes; D051381:Rats; D011919:Rats, Inbred Strains; D012441:Saccharomyces cerevisiae / Q000235:genetics*; D012689:Sequence Homology, Nucleic Acid; D014157:Transcription Factors / Q000235:genetics*
D023081:CCAAT-Binding Factor; D022762:CCAAT-Enhancer-Binding Proteins; D004268:DNA-Binding Proteins; D005656:Fungal Proteins; D046911:Macromolecular Substances; D015345:Oligonucleotide Probes; D014157:Transcription Factors