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Recently, a new class of homeobox genes has been identified, called LIM-homeobox genes. These genes encode proteins which have two tandemly repeated cysteine motifs, referred to as LIM domains, in addition to a homeodomain. In addition, proteins with only LIM domains have been described but the function of the LIM domain is unknown. We have analysed the function of LIM domains using Isl-1 as a representative LIM-homeodomain protein. Employing protein prepared in bacterial cells, we show that the presence of the LIM domain in Isl-1 inhibits binding of the homeodomain to its DNA target. This in vitro inhibition can be released either by denaturation/renaturation of the protein or by truncation of the LIM domains. A similar inhibition is observed in vivo using reporter constructs. In addition we show that LIM domains in a chimeric protein can inhibit binding of the Ubx homeodomain to its target. The ability of LIM domains to inhibit DNA binding by the homeodomain provides a possible basis for negative regulation of LIM-homeodomain proteins in vivo.

Type

Journal article

Journal

EMBO J

Publication Date

11/1993

Volume

12

Pages

4243 - 4250

Keywords

Base Sequence, Binding Sites, Cysteine, DNA Mutational Analysis, DNA-Binding Proteins, Drosophila Proteins, Endopeptidase K, Gene Expression Regulation, Genes, Homeobox, Genes, Reporter, Homeodomain Proteins, LIM-Homeodomain Proteins, Molecular Sequence Data, Multigene Family, Nerve Tissue Proteins, Protein Conformation, Recombinant Fusion Proteins, Regulatory Sequences, Nucleic Acid, Serine Endopeptidases, Structure-Activity Relationship, Transcription Factors, Transcriptional Activation