NFI-B3, a novel transcriptional repressor of the nuclear factor I family, is generated by alternative RNA processing.
Nuclear factor I (NFI) proteins constitute a family of sequence-specific transcription factors whose functional diversity is generated through transcription from four different genes (NFI-A, NFI-B, NFI-C, and NFI-X), alternative RNA splicing, and protein heterodimerization. Here we describe a naturally truncated isoform, NFI-B3, which is derived from the human NFI-B gene, in addition to characterizing further human NFI-B1 and NFI-B2, two differentially spliced variants previously isolated from hamster and chicken. Although NFI-B1 and NFI-B2 proteins are translated from an 8. 7-kilobase message, the mRNA for NFI-B3 has a size of only 1.8 kilobases. The NFI-B3 message originates from the failure to excise the first intron downstream of the exons encoding the DNA binding domain and subsequent processing of this transcript at an intron-internal polyadenylation signal. The translation product includes the proposed DNA binding and dimerization domain and terminates after translation of two additional "intron" encoded codons. In SL-2 cells, which are void of endogenous NFI, NFI-B3 by itself had no effect on transcriptional regulation and failed to bind DNA. Coexpression of NFI-B3 with other isoforms of the NFI-B, -C, and -X family, however, led to a strong reduction of transcriptional activation compared with the expression of these factors alone. Gel shift analysis indicated that NFI-B3 disrupts the function of other NFI proteins by reducing their DNA binding activity by heterodimer formation. The efficiency of NFI-B3 heterodimers to bind to DNA correlated with the degree of transcriptional repression. The abundance of NFI-B transcripts varied significantly between different human cell lines and tissues, suggesting a potential involvement of these factors in the complex mechanisms that generate cell type specificity.
Liu
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Institute of Molecular and Cell Biology, National University of Singapore, Singapore 119260, USA.
Bernard
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HU
Apt
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D017398:Alternative Splicing; D000818:Animals; D022762:CCAAT-Enhancer-Binding Proteins; D002460:Cell Line; D002467:Cell Nucleus / Q000378:metabolism; D002645:Chickens; D003001:Cloning, Molecular; D006224:Cricetinae; D004268:DNA-Binding Proteins / Q000096:biosynthesis*; D005091:Exons; D014644:Genetic Variation; D006367:HeLa Cells; D006801:Humans; D007438:Introns; D051839:NFI Transcription Factors; D009687:Nuclear Proteins; D016133:Polymerase Chain Reaction; D014176:Protein Biosynthesis; D012333:RNA, Messenger / Q000378:metabolism; D011994:Recombinant Proteins / Q000096:biosynthesis; D012097:Repressor Proteins / Q000096:biosynthesis* / Q000235:genetics; D014157:Transcription Factors; D014158:Transcription, Genetic; D051840:Y-Box-Binding Protein 1
D022762:CCAAT-Enhancer-Binding Proteins; D004268:DNA-Binding Proteins; D051839:NFI Transcription Factors; C497592:NFIA protein, human; C497647:NFIC protein, human; D009687:Nuclear Proteins; D012333:RNA, Messenger; D011994:Recombinant Proteins; D012097:Repressor Proteins; D014157:Transcription Factors; D051840:Y-Box-Binding Protein 1; C070856:YBX1 protein, human