The GA octodinucleotide repeat binding factor BBR participates in the transcriptional regulation of the homeobox gene Bkn3.
In the dominant mutant Hooded (K), the barley gene BKn3 is overexpressed as a result of a duplication of 305 bp in intron IV. When fused to a cauliflower mosaic virus 35S minimal promoter, the 305 bp element activates gene expression in tobacco, as does a 655 bp BKn3 promoter sequence. Both DNA fragments contain a (GA)8 repeat (GA/TC)8. A one-hybrid screen using the 305 bp element as the DNA target led to the cloning of the barley b recombinant (BBR) protein, which binds specifically to the (GA/TC)8 repeat. BBR is nuclear targeted and is a characterized nuclear localization signal (NLS) sequence, a DNA-binding domain extended up to 90 aa at the C-terminus and a putative N-terminal activation domain. The corresponding gene has no introns and is ubiquitously expressed in barley tissues. In co-transfection experiments, BBR activates (GA/TC)8-containing promoters, and its overexpression in tobacco leads to a pronounced leaf shape modification. BBR has properties of a GAGA-binding factor, but the corresponding gene has no sequence homology to Trl and Psq of Drosophila, which encode functionally analogous proteins. In Arabidopsis, (GA/TC)8 repeats occur particularly within 1500 bp upstream of gene start codons included in some homeodomain genes of different classes. The data presented suggest that expression of the barley BKn3 is regulated, at least in part, by the binding of the transcription factor BBR to GA/TC repeats.
Santi
Luca
L
Max-Planck-Institut für Züchtungsforschung, Department of Plant Breeding and Yield Physiology, Carl-von-Linné-Weg 10, 50829 Köln, Germany.
Wang
Yamei
Y
Stile
Maria Rosaria
MR
Berendzen
Kenneth
K
Wanke
Dierk
D
Roig
Cristina
C
Pozzi
Carlo
C
Müller
Kai
K
Müller
Judith
J
Rohde
Wolfgang
W
Salamini
Francesco
F
D000595:Amino Acid Sequence; D019295:Computational Biology; D004268:DNA-Binding Proteins / Q000378:metabolism; D004742:Enhancer Elements, Genetic / Q000235:genetics; D018506:Gene Expression Regulation, Plant; D005801:Genes, Homeobox / Q000235:genetics*; D017343:Genes, Plant / Q000235:genetics*; D001467:Hordeum / Q000235:genetics*; D007438:Introns / Q000235:genetics; D008969:Molecular Sequence Data; D019913:Nuclear Localization Signals; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D011401:Promoter Regions, Genetic; D012091:Repetitive Sequences, Nucleic Acid; D017386:Sequence Homology, Amino Acid; D014026:Nicotiana / Q000235:genetics; D014158:Transcription, Genetic; D015533:Transcriptional Activation; D015003:Yeasts
D004268:DNA-Binding Proteins; D019913:Nuclear Localization Signals; D010940:Plant Proteins