Intramolecular control of transcriptional activity by the NK2-specific domain in NK-2 homeodomain proteins.
The developmentally important homeodomain transcription factors of the NK-2 class contain a highly conserved region, the NK2-specific domain (NK2-SD). The function of this domain, however, remains unknown. The primary structure of the NK2-SD suggests that it might function as an accessory DNA-binding domain or as a protein-protein interaction interface. To assess the possibility that the NK2-SD may contribute to DNA-binding specificity, we used a PCR-based approach to identify a consensus DNA-binding sequences for Nkx2.2, an NK-2 family member involved in pancreas and central nervous system development. The consensus sequence (T(C)(T)AAGT(G)(A)(G)(C)TT) is similar to the known binding sequences for other NK-2 homeodomain proteins, but we show that the NK2-SD does not contribute significantly to specific DNA binding to this sequence. To determine whether the NK2-SD contributes to transactivation, we used GAL4-Nkx2. 2 fusion constructs to map a powerful transcriptional activation domain in the C-terminal region beyond the conserved NK2-SD. Interestingly, this C-terminal region functions as a transcriptional activator only in the absence of an intact NK2-SD. The NK2-SD also can mask transactivation from the paired homeodomain transcription factor Pax6, but it has no effect on transcription by itself. These results demonstrate that the NK2-SD functions as an intramolecular regulator of the C-terminal activation domain in Nkx2.2 and support a model in which interactions through the NK2-SD regulate the ability of NK-2-class proteins to activate specific genes during development.
Watada
H
H
Hormone Research Institute and Department of Medicine, University of California, San Francisco 94143-0534, USA.
Mirmira
R G
RG
Kalamaras
J
J
German
M S
MS
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D001665:Binding Sites; D002460:Cell Line; D016384:Consensus Sequence / Q000235:genetics; D017124:Conserved Sequence; D004247:DNA / Q000235:genetics / Q000378:metabolism; D017930:Genes, Reporter / Q000235:genetics; D018398:Homeodomain Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D017434:Protein Structure, Tertiary; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D012097:Repressor Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D020218:Response Elements / Q000235:genetics; D016415:Sequence Alignment; D017384:Sequence Deletion / Q000235:genetics; D015534:Trans-Activators / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic / Q000235:genetics*; D015533:Transcriptional Activation / Q000235:genetics
D018398:Homeodomain Proteins; D011993:Recombinant Fusion Proteins; D012097:Repressor Proteins; D015534:Trans-Activators; D004247:DNA