Mutations that affect the ability of the vnd/NK-2 homeoprotein to regulate gene expression: transgenic alterations and tertiary structure.
The importance in downstream target regulation of tertiary structure and DNA binding specificity of the protein encoded by the vndNK-2 homeobox gene is analyzed. The ectopic expression patterns of WT and four mutant vndNK-2 genes are analyzed together with expression of two downstream target genes, ind and msh, which are down-regulated by vndNK-2. Three mutants are deletions of conserved regions (i.e., tinman motif, acidic motif, and NK-2 box), and the fourth, Y54M vndNK-2, corresponds to a single amino acid residue replacement in the homeodomain. Of the four ectopically expressed mutant genes examined, only the Y54M mutation inactivates the ability of the vndNK-2 homeodomain protein to repress ind and msh. The acidic motif deletion mutant slightly reduced the ability of the protein to repress ind and msh. By contrast, both tinman and NK-2 box deletion mutants behaved as functional vndNK-2 genes in their ability to repress ind and msh. The NMR-determined tertiary structures of the Y54M vndNK-2 homeodomain, both free and bound to DNA, are compared with the WT analog. The only structural difference observed for the mutant homeodomain is in the complex with DNA and involved closer interaction of the methionine-54 with A2, rather than with C3 of the (-) strand of the DNA. This subtle change in the homeodomain-DNA complex resulted in modifications of binding affinities to DNA. These changes resulting from a single amino acid residue replacement constitute the molecular basis for the phenotypic alterations observed on ectopic expression of the Y54M vndNK-2 gene during embryogenesis.
Koizumi
Keita
K
Neural Cell-Fate Determinants Section, National Institute of Neurological Diseases and Stroke, Building 36, Room 3C17, National Institutes of Health, Bethesda, MD 20892-4130, USA.
Lintas
Carla
C
Nirenberg
Marshall
M
Maeng
Jin-Soo
JS
Ju
Jeong-Ho
JH
Mack
James W
JW
Gruschus
James M
JM
Odenwald
Ward F
WF
Ferretti
James A
JA
D019943:Amino Acid Substitution; D000818:Animals; D030801:Animals, Genetically Modified; D001483:Base Sequence; D001665:Binding Sites / Q000235:genetics; D004247:DNA / Q000235:genetics / Q000378:metabolism; D029721:Drosophila Proteins / Q000737:chemistry / Q000235:genetics*; D004331:Drosophila melanogaster / Q000196:embryology / Q000235:genetics*; D018507:Gene Expression Regulation, Developmental; D005801:Genes, Homeobox; D017344:Genes, Insect; D018398:Homeodomain Proteins / Q000737:chemistry / Q000235:genetics*; D008958:Models, Molecular; D009154:Mutation; D010641:Phenotype; D017434:Protein Structure, Tertiary; D014157:Transcription Factors
D029721:Drosophila Proteins; D018398:Homeodomain Proteins; D014157:Transcription Factors; C094797:vnd protein, Drosophila; D004247:DNA