Sp1 activates the transcription of many cellular and viral genes with the GC-box in either the proximal promoter or the enhancer. Sp1 is composed of several functional domains, such as the inhibitory domain (ID), two serine/threonine-rich domains, two glutamine-rich domains, three C 2 H 2 -type zinc finger DNA binding domains (ZFDBD), and a C-terminal D domain. The ZDDBD is the most highly conserved domain among the Sp-family transcription factors and plays a critical role in GCbox recognition. In this study, we investigated the protein-protein interactions occurring at the Sp1ZFDBD and the Sp1ID, and the molecular mechanisms controlling the interaction. Our results found that Sp1ZFDBD and Sp1ID repressed transcription once they were targeted to the proximal promoter of the pGal4 UAS reporter fusion gene system, suggesting molecular interaction with the repressor molecules. Indeed, mammalian two-hybrid assays, GST fusion protein pull-down assays, and co-immunoprecipitation assays showed that Sp1ZFDBD and Sp1ID are able to interact with corepressor proteins such as SMRT, NcoR, and BCoR. The molecular interactions appear to be regulated by MAP kinase/Erk kinase kinase (MEK). The molecular interactions between Sp1ID and the corepressor might explain the role of Sp1 as a repressor under certain circumstances. The siRNA-induced degradation of the corepressors resulted in an up-regulation of Sp1-dependent transcription. The cellular context of the corepressors and the regulation of molecular interaction between corepressors and Sp1ZFDBD or Sp1ID might be important in controlling Sp1 activity.Transcriptional regulation of the eukaryotic gene is a complicated process, involving a series of complex molecular interactions among regulatory and transcription factors. Specificity protein 1 (Sp1) 1 is probably one of the best characterized sequence-specific transcription factors, and has numerous functions in the transcription of many cellular and viral genes harboring GC boxes in their promoters (1, 2). Sp1 and its family of proteins have been implicated in a host of essential biological processes, and have been proven important in apoptosis, cell growth inhibition, differentiation, and carcinogenesis (Refs. 3-5 and references therein).Sp1 is a member of the Sp-multigene family, which also includes Sp2, Sp3, Sp4, Sp5, Sp6, Sp7, and Sp8 (3-5). The Sp-family proteins exhibit similar domain structures and are evolutionarily closely related. All of these proteins possess highly conserved C 2 H 2 -type zinc finger DNA binding domains at their C termini, and all belong to the Krü ppel-like zinc finger superfamily (3-5). In addition, the Sp-family proteins have been demonstrated to undergo post-translational modifications as the result of diverse mechanisms. For example, Sp1 is glycosylated and phosphorylated by Erk2, protein kinase C, casein kinase II, and cAMP-dependent protein kinase; Sp3 is acetylated and SUMOylated by the protein inhibitor of activated STAT (PIAS1, Ref. 3 and references therein, Refs. 6 -10).The Sp1 protein co...

In this work atomic layer deposition of Al2O3 and TiO2 has been used to obtain dielectric stacks for passivation of silicon surfaces. Our experiments on n‐ and p‐type silicon wafers deposited by thin Al2O3/TiO2 stacks show that a considerably improved passivation is obtained compared to the Al2O3 single layer. For Al2O3 films thinner than 20 nm the emitter saturation current density decreases with increasing TiO2 thickness. Especially the passivation of ultrathin (∼5 nm) Al2O3 is very effectively enhanced by TiO2 due to a decreased interface defect density as well as an increased fixed negative charge in the stacks. Hence, the thin Al2O3/TiO2 stacks developed in this work can be used as a passivation coating for Si‐based solar cells. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

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