Repression of major histocompatibility complex I-A beta gene expression by dbpA and dbpB (mYB-1) proteins.
The induction of major histocompatibility complex class II gene expression is mediated by three DNA elements in the promoters of these genes (W, X, and Y boxes). The Y box contains an inverted CCAAT box sequence, and the binding activity to the CAAT box is mediated by factor NF-Y, which is composed of subunits NF-YA and NF-YB. We have found that transfection of either dbpA or dbpB (mYB-1) or both inhibits I-A beta gene expression. Although the genes for some members of the Y-box family of binding proteins have been isolated by screening an expression library using the Y-box sequence, under our conditions no binding of dbpA or dbpB to the Y box of the I-A beta or I-E alpha promoter was detected. This suggested that repression of I-A beta gene expression by dbpA and dbpB was not due to competition for binding to the Y-box sequence. The results suggest two other mechanisms by which dbpA and dbpB can inhibit transcription from the I-A beta promoter. When dbpA was added, the binding of NF-YA to DNA increased, which could be explained by interaction between these two proteins whose purpose is to increase the binding affinity of NF-YA for DNA. However, this complex was unable to stimulate transcription from the I-A beta promoter. Thus, dbpA competed for the interaction between NF-YA and NF-YB by binding to NF-YA. When dbpB factor was added together with NF-YA and NF-YB, the binding of the NF-YA--NF-YB complex was reduced. This suggested that dbpB may complete with NF-YB for interaction with NF-YA. These results provide an example of how dbpA and dbpB may regulate transcription of promoters that utilize NF-Y as a transcription factor.
Lloberas
J
J
Departament de Fisiologia (Immunologia), Facultat de Biologia, Barcelona, Spain.
Maki
R A
RA
Celada
A
A
D001402:B-Lymphocytes / Q000187:drug effects / Q000276:immunology*; D001483:Base Sequence; D001667:Binding, Competitive; D022762:CCAAT-Enhancer-Binding Proteins; D004268:DNA-Binding Proteins / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D005786:Gene Expression Regulation; D005802:Genes, MHC Class II / Q000235:genetics*; D006360:Heat-Shock Proteins / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D007371:Interferon-gamma / Q000494:pharmacology; D008969:Molecular Sequence Data; D051839:NFI Transcription Factors; D011401:Promoter Regions, Genetic / Q000235:genetics; D011485:Protein Binding; D011994:Recombinant Proteins / Q000378:metabolism; D014157:Transcription Factors; D014158:Transcription, Genetic; D015533:Transcriptional Activation
D022762:CCAAT-Enhancer-Binding Proteins; D004268:DNA-Binding Proteins; D006360:Heat-Shock Proteins; D051839:NFI Transcription Factors; D011994:Recombinant Proteins; D014157:Transcription Factors; D007371:Interferon-gamma