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Nuclear factor I (NF-I) or CCAAT box-binding transcription factor (CTF) [1,2]
(also known as TGGCA-binding proteins) are a family of vertebrate nuclear
proteins which recognize and bind, as dimers, the palindromic DNA sequence
5'-TTGGCNNNNNGCCAA-3'. CTF/NF-I binding sites are present in viral and
cellular promoters and in the origin of DNA replication of Adenovirus type 2.
The CTF/NF-I proteins were first identified as nuclear factor I, a collection
of proteins that activate the replication of several Adenovirus serotypes
(together with NF-II and NF-III) . The family of proteins was also
identified as the CTF transcription factors, before the NFI and CTF families
were found to be identical . The CTF/NF-I proteins are individually capable
of activating transcription and DNA replication. The CTF/NF-I family name has
also been dubbed as NFI, NF-I or NF1.
In a given species, there are a large number of different CTF/NF-I proteins.
The multiplicity of CTF/NF-I is known to be generated both by alternative
splicing and by the occurrence of four different genes. The known forms of
NF-I genes have been classified as:
The CTF-like factors subfamily (prototype form: CTF-1) 
The NFI-X proteins.
The NFI-A proteins.
The NFI-B proteins.
So far, all CTF/NF-I family members appear to have similar transcription and
CTF/NF-I proteins contains 400 to 600 amino acids. The N-terminal 200 amino-acid sequence, almost perfectly conserved in all species and genes sequenced,
mediates site-specific DNA recognition, protein dimerization and Adenovirus
DNA replication. The C-terminal 100 amino acids contain the transcriptional
activation domain. This activation domain is the target of gene expression
regulatory pathways ellicited by growth factors and it interacts with basal
transcription factors and with histone H3 .
The CTF/NF-I DNA-binding domain contains four conserved Cys residues, which
are required for its DNA-binding activity .
As a specific signature for this family of proteins, we selected a perfectly
conserved, highly charged 12 residue peptide located in the DNA-binding domain
of CTF/NF-I. We also developed a profile that covers the entire CTF/NF-I DNA-binding domain.
It has been said that the CTF/NF-I DNA-binding domain might be related
to the MH1 domain (see <PDOC51075>) [8,9].
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