Lymphoid enhancer-binding factor 1 (LEF-1) belongs to the LEF-1/TCFs (T cell factors) family of transcription factors []. LEF-1 participates in the Wnt signalling pathway, performing its function in complexes with beta-catenin [, , ]. LEF-1 may also acquire diverse regulatory functions by association with Wnt/beta-catenin-independent stimuli, such as the TGF-beta and Notch pathways [, ].
High mobility group (HMG) box domains are involved in binding DNA, and may be involved in protein-protein interactions as well. The structure of the HMG-box domain consists of three helices in an irregular array. HMG-box domains are found in one or more copies in HMG-box proteins, which form a large, diverse family involved in the regulation of DNA-dependent processes such as transcription, replication, and strand repair, all of which require the bending and unwinding of chromatin. Many of these proteins are regulators of gene expression. HMG-box proteins are found in a variety of eukaryotic organisms, and can be broadly divided into two groups, based on sequence-dependent and sequence-independent DNA recognition; the former usually contain one HMG-box motif, while the latter can contain multiple HMG-box motifs.HMG-box domains can be found in single or multiple copies in the following protein classes: HMG1 and HMG2 non-histone components of chromatin; SRY (sex determining region Y protein) involved in differential gonadogenesis; the SOX family of transcription factors []; sequence-specific LEF1 (lymphoid enhancer binding factor 1) and TCF-1 (T-cell factor 1) involved in regulation of organogenesis and thymocyte differentiation []; structure-specific recognition protein SSRP involved in transcription and replication; MTF1 mitochondrial transcription factor; nucleolar transcription factors UBF 1/2 (upstream binding factor) involved in transcription by RNA polymerase I; Abf2 yeast ARS-binding factor []; yeast transcription factors lxr1, Rox1, Nhp6b and Spp41; mating type proteins (MAT) involved in the sexual reproduction of fungi []; and the YABBY plant-specific transcription factors.
High mobility group (HMG) box domains are involved in binding DNA, and may be involved in protein-protein interactions as well. The structure of the HMG-box domain consists of three helices in an irregular array. HMG-box domains are found in one or more copies in HMG-box proteins, which form a large, diverse family involved in the regulation of DNA-dependent processes such as transcription, replication, and strand repair, all of which require the bending and unwinding of chromatin. Many of these proteins are regulators of gene expression. HMG-box proteins are found in a variety of eukaryotic organisms, and can be broadly divided into two groups, based on sequence-dependent and sequence-independent DNA recognition; the former usually contain one HMG-box motif, while the latter can contain multiple HMG-box motifs.HMG-box domains can be found in single or multiple copies in the following protein classes: HMG1 and HMG2 non-histone components of chromatin; SRY (sex determining region Y protein) involved in differential gonadogenesis; the SOX family of transcription factors []; sequence-specific LEF1 (lymphoid enhancer binding factor 1) and TCF-1 (T-cell factor 1) involved in regulation of organogenesis and thymocyte differentiation []; structure-specific recognition protein SSRP involved in transcription and replication; MTF1 mitochondrial transcription factor; nucleolar transcription factors UBF 1/2 (upstream binding factor) involved in transcription by RNA polymerase I; Abf2 yeast ARS-binding factor []; yeast transcription factors lxr1, Rox1, Nhp6b and Spp41; mating type proteins (MAT) involved in the sexual reproduction of fungi []; and the YABBY plant-specific transcription factors. Structurally, the HMG box domain is composed of three helices.
SUMO proteins are ubiquitin like proteins that are covalently attached to and detached from other proteins in cells to modify their function. SUMO is first activated in an ATP-dependent reaction by formation of a thioester bond with an E1 (SUMO-activating) enzyme and then transferred to the SUMO conjugating (E2) enzyme Ubc9. Ubc9 catalyses the formation of an isopeptide bond between the C-terminal of SUMO and the amino group of lysine in the target protein. Sumoylated proteins can be targeted for different cellular processes, such as nuclear transport, transcriptional regulation, apoptosis, and protein stability []. PIAS4 is an E3-type small ubiquitin-like modifier (SUMO) ligase, stabilising the interaction between Ubc9 and the substrate, and is a SUMO-tethering factor []. It plays a crucial role as a transcriptional coregulation in various cellular pathways, including the STAT pathway, the p53/TP53 pathway, the Wnt pathway and the steroid hormone signaling pathway. It mediates sumoylation of CEBPA, PARK7, HERC2, MYB, TCF4 and RNF168. In Wnt signaling, represses LEF1 and enhances TCF4 transcriptional activities through promoting their sumoylations [, , , , ].
