Interaction between two homeodomain proteins is specified by a short C-terminal tail.
Two yeast homeodomain proteins, a1 and alpha 2, interact and cooperatively bind the haploid-specific gene (hsg) operator, resulting in the repression of a set of genes involved in the determination of cell type. The cooperative binding of a1 and alpha 2 to DNA can be reconstituted in vitro using purified fragments of a1 and alpha 2. Only the homeodomain is needed for a1, but for alpha 2 a C-terminal 22-amino-acid tail is required as well. As most of the specificity of DNA binding appears to derive from a1, we proposed that alpha 2 functions in the a1/alpha 2 heterodimer to contact a1 with its tail. By construction and analysis of several chimaeric proteins, we investigate how two DNA-binding proteins, one with low intrinsic specificity (alpha 2) and one with no apparent intrinsic DNA-binding ability (a1), can together create a highly specific DNA-binding activity. We show that the 22-amino-acid region of alpha 2 immediately C-terminal to the homeodomain, when grafted onto the a1 homeodomain, converts a1 to a strong DNA-binding protein. This alpha 2 tail can also be attached to the Drosophila engrailed homeodomain, and the chimaeric protein now binds cooperatively to DNA with a1, showing how a simple change can create a new homeodomain combination that specifically recognizes a new DNA operator.
Stark
M R
MR
Department of Biochemistry and Biophysics, School of Medicine, University of California, San Francisco 94143-0502.
Johnson
A D
AD
D000818:Animals; D001483:Base Sequence; D029742:Caenorhabditis elegans Proteins; D003001:Cloning, Molecular; D004247:DNA / Q000138:chemical synthesis / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000378:metabolism*; D004330:Drosophila; D029721:Drosophila Proteins; D004926:Escherichia coli; D005656:Fungal Proteins / Q000378:metabolism*; D015801:Helminth Proteins / Q000378:metabolism; D018398:Homeodomain Proteins; D007301:Insect Hormones / Q000378:metabolism; D060850:LIM-Homeodomain Proteins; D026341:Minichromosome Maintenance 1 Protein; D015778:Minor Histocompatibility Antigens; D008969:Molecular Sequence Data; D009875:Operator Regions, Genetic; D050809:POU Domain Factors; D011485:Protein Binding; D011487:Protein Conformation; D019253:Proto-Oncogene Proteins c-bcl-2; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D051818:Replication Protein C; D012097:Repressor Proteins; D029701:Saccharomyces cerevisiae Proteins; D014157:Transcription Factors / Q000378:metabolism
C096816:BCL2-related protein A1; D029742:Caenorhabditis elegans Proteins; D004268:DNA-Binding Proteins; D029721:Drosophila Proteins; C063459:En protein, Drosophila; D005656:Fungal Proteins; D015801:Helminth Proteins; D018398:Homeodomain Proteins; D007301:Insect Hormones; D060850:LIM-Homeodomain Proteins; C096063:MATA1 protein, S cerevisiae; C062928:MATA2 protein, S cerevisiae; D026341:Minichromosome Maintenance 1 Protein; D015778:Minor Histocompatibility Antigens; D050809:POU Domain Factors; D019253:Proto-Oncogene Proteins c-bcl-2; D011993:Recombinant Fusion Proteins; D012097:Repressor Proteins; D029701:Saccharomyces cerevisiae Proteins; D014157:Transcription Factors; C072005:mec-3 protein, C elegans; C081539:unc-86 protein, C elegans; D004247:DNA; D051818:Replication Protein C