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    DNA affinity cleaving analysis of homeodomain-DNA interaction: identification of homeodomain consensus sites in genomic DNA.
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    Abstract:
    We have incorporated the DNA-cleaving moiety o-phenanthroline-copper at amino acid 10 of the Msx-1 homeodomain, and we have analyzed site-specific DNA cleavage by the resulting Msx-1 derivative. We show that amino acid 10 of the Msx-1 homeodomain is close to the 5' end of the consensus DNA site 5'-(C/G)TAATTG-3' in the Msx-1-DNA complex. Our results indicate that the orientation of the Msx-1 homeodomain relative to DNA is analogous to the orientation of the engrailed and Antennapedia homeodomains. We show further that DNA affinity cleaving permits identification of consensus DNA sites for Msx-1 in kilobase DNA substrates. The specificity of the approach enabled us to identify an Msx-1 consensus DNA site within the transcriptional control region of the developmental regulatory gene Wnt-1. We propose that incorporation of o-phenanthroline-copper at amino acid 10 of a homeodomain may provide a generalizable strategy to determine the orientation of a homeodomain relative to DNA and to identify homeodomain consensus DNA sites in genomic DNA.
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    engrailed
    In U. maydis the multiallelic b locus controls sexual and pathogenic development. In the b locus a gene coding for a regulatory protein had been identified, and it was suggested that the interaction of two b polypeptides specified by different alleles programs sexual development in this fungus. We now demonstrate the existence of a second regulatory gene in the b locus. We term this gene bW and refer to the former as the bE gene. Both genes exist in many alleles. Although unrelated in primary sequence, both genes are similar in their overall organization. The gene products display allele-specific variability in their N-terminal domains, show a high degree of sequence conservation in the C-terminal domains, and contain a homeodomain-related motif. Genetic evidence is provided to show that the pair of bE and bW polypeptides encoded by different b alleles is the key regulatory species.
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    Abstract The A mating type locus of Coprinus cinereus determines mating compatibility by regulating essential steps in sexual development. Each A locus contains several genes separated into two functionally independent complexes termed Aα and Aβ, and the multiple alleles of these genes generate an estimated 160 A mating specificities. The genes encode two classes of homeodomain-containing proteins designated HD1 and HD2. In this report we describe two newly cloned loci, A2 and A5, and compare them with A42, A43 and A6 that we have described previously. An Aβ-null locus, retaining just a single active HD1 gene from the α-complex, was generated by mutation. Using this as a transformation host, gene combinations that promote A-regulated development were identified. We demonstrate that each A locus contains members of three paralogous pairs of HD1 and HD2 genes. Different allelic versions of gene pairs are compatible but paralogous genes are incompatible. The genes present in four uncloned A loci were deduced using Southern analyses and transformations with available cloned genes. The combined analysis of nine A factors identifies sufficient A gene alleles to generate at least 72 A mating specificities.
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    Mouse genes containing homeo box domains are predicted to fulfill important functions in embryogenesis. Using recombinant inbred mouse strains, we have mapped a mouse gene which contains a homeo box with homology to the Drosophila engrailed gene. This gene maps to mouse chromosome 1 near or at the dominant hemimelia locus which is a known mouse developmental mutation.
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    The zebrafish genome was found to contain two sequences which cross-hybridize strongly with the engrailed gene of Drosophila. Several independent clones containing one of these cross-hybridizing sequences were isolated from a zebrafish genomic library. Characterization of this region (ZF-EN) by DNA sequencing showed that it shares about 70% sequence identity with the engrailed homeobox. More extensive homeobox homology (greater than 90%) was found relative to the murine En genes. The closest relationship exists between ZF-EN and En-2 where the C-terminal domains (104 amino acids) encoded by these genes are almost identical. We also observed that ZF-EN and En-2 are very similar with respect to their transcript sizes and temporal expression patterns.
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    Forelimbs and hindlimbs of tetrapods have different morphological patterns. One plausible explanation for the difference is that the cells that give rise to the limbs differentially express genes which control their pattern of development. Amphibian limb regeneration is an excellent system to test this hypothesis, since the same ultimate morphology is attained in regeneration as through embryogenesis. Using a combination of homeobox probes and differential screening, I have isolated two newt genes which are differentially expressed in regenerating forelimbs and hindlimbs. One of these genes displays properties expected of a gene involved in controlling limb morphology, including expression in mesodermal tissue and constancy of expression upon transplantation. Based on sequence analysis, this gene appears to be homologous to a homeobox-containing gene previously isolated from frog and human libraries.
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    The homeodomain (HD) is a conserved sequence-specific DNA-binding motif found in many eukaryotic transcriptional regulatory proteins. Despite the wealth of in vitro data on the mechanism HD proteins use to bind DNA, comparatively little is known about the roles of individual residues in these domains in vivo . The Saccharomyces cerevisiae Pho2 protein contains a HD that shares significant sequence identity with the Drosophila Engrailed protein. We have used the co-crystal structure of Engrailed as a model to predict how Pho2 might contact DNA and have examined how individual residues of the Pho2 HD contribute to transcriptional activation in vivo and to DNA binding in vitro . Our results demonstrate that Pho2 and Engrailed share many similar DNA-binding characteristics. However, our results also show that some highly conserved residues, which contact the DNA in many HD structures, make relatively small contributions to the DNA-binding affinity and in vivo activity of the Pho2 protein. We also show that the N-terminal arm of the Pho2 HD is a critical component in determining the DNA-binding specificity of the protein and that the requirements for residues in the N-terminal arm are promoter-dependent for Pho2 transcriptional activation and DNA binding.
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