We describe a novel human cDNA isolated by target site screening of a placental expression library, using as a probe, an essential element of a TATA box-less promoter corresponding to a pregnancy-specific glycoprotein gene. The cDNA encoded a predicted protein of 290 amino acids, designated core promoter-binding protein (CPBP), which has three zinc fingers (type Cys 2 -His 2 ) at the end of its C-terminal domain, a serine/threonine-rich central region and an acidic domain lying within the N-terminal region. Additional sequence analysis and data base searches revealed that only the zinc finger domains are conserved (60 -80% identity) in other transcription factors. In cotransfection assays, CPBP increased the transcription from a minimal promoter containing its natural DNA-binding site. Moreover, a chimeric protein between CPBP and Gal4 DNA binding domain also increased the activity of an heterologous reporter gene containing Gal4 DNA binding sites. The tissue distribution analysis of CPBP mRNA revealed that it is differentially expressed with an apparent enrichment in placental cells. The DNA binding and transcriptional activity of CPBP, in conjunction with its expression pattern, strongly suggests that this protein may participate in the regulation and/or maintenance of the basal expression of PSG and possibly other TATA box-less genes.The molecular mechanisms involved in the transcription of eukaryotic genes are controlled by the ordered interplay of DNA-protein and protein-protein contacts. The factors responsible for basal RNA-polymerase II transcription reaction are the core promoter elements and the general transcription factors (1, 2). In addition, the regulation of transcription rates results from the combined action of activating and repressing proteins that are brought to promoters, enhancers, and silencers through their interactions with specific sequences and sub-

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Nitric oxide is a ubiquitous free radical that plays a key role in a broad spectrum of signaling pathways in physiological and pathophysiological processes. We have explored the transcriptional regulation of inducible nitric-oxide synthase (iNOS) by Krü ppel-like factor 6 (KLF6), an Sp1-like zinc finger transcription factor. Study of serial deletion constructs of the iNOS promoter revealed that the proximal 0.63-kb region can support a 3-6-fold reporter activity similar to that of the fulllength 16-kb promoter. Within the 0.63-kb region, we identified two CACCC sites (؊164 to ؊168 and ؊261 to ؊265) that bound KLF6 in both electrophoretic mobility shift and chromatin immunoprecipitation assays. Mutation of both these sites abrogated the KLF6-induced enhancement of the 0.63-kb iNOS promoter activity. The binding of KLF6 to the iNOS promoter was significantly increased in Jurkat cells, primary T lymphocytes, and COS-7 cells subjected to NaCN-induced hypoxia, heat shock, serum starvation, and phorbol 12-myristate 13-acetate/A23187 ionophore stimulation. Furthermore, in KLF6-transfected and NaCN-treated COS-7 cells, there was a 3-4-fold increase in the expression of the endogenous iNOS mRNA and protein that correlated with increased production of nitric oxide. These findings indicate that KLF6 is a potential transactivator of the human iNOS promoter in diverse pathophysiological conditions. Nitric-oxide synthases are key proteins that produce NO and thereby regulate many important biological processes. NO is generated during the oxidation of L-arginine to L-citrulline by at least three different isoforms of nitric-oxide synthase. Endothelial and neuronal nitric-oxide synthases are constitutively expressed, and their activity is Ca 2ϩ -and calmodulin-dependent, whereas the third isoform is transcriptionally inducible (iNOS), 1 and its activity is independent of Ca 2ϩ and calmodulin and can produce very high levels of nitric oxide over a sustained period of time (1, 2). It has been shown that iNOS is transcriptionally up-regulated in pathophysiologic conditions such as hypoxia, ischemia-reperfusion injury, and trauma and by reactive oxygen species (3, 4).

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