contributed equally to this work STAT factors act as signal transducers of cytokine receptors and transcriptionally activate speci®c target genes. The recently discovered protein PIAS3 binds directly to STAT3 and blocks transcriptional activation. Here, we present experimental evidence implementing the zinc ®nger protein G®-1 as a new regulatory factor in STAT3-mediated signal transduction. The interaction between the two proteins ®rst became evident in a yeast two-hybrid screen but was also seen in coprecipitation experiments from eukaryotic cells. Moreover, we found that both G®-1 and PIAS3 colocalize in a characteristic nuclear dot structure. While PIAS3 exerts a profound inhibitory effect on STAT3-mediated transcription of target promoters, G®-1 can overcome the PIAS3 block and signi®cantly enhances STAT3-mediated transcriptional activation. In primary T cells, G®-1 was able to amplify IL-6-dependent T-cell activation. As G®-1 is a known, dominant proto-oncogene, our ®ndings bear particular importance for the recently described ability of STAT3 to transform cells malignantly and offer an explanation of the oncogenic potential of G®-1 in T lymphocytes.

The TRPS1 gene codes for a 1281 amino acids nuclear transcription factor with an unusual combination of different types of zinc finger motifs, including GATA-type DNA-binding and IKAROS-like zinc fingers. TRPS1 is a repressor of GATA-regulated genes and implicated in the human tricho-rhino-phalangeal syndromes. We found that two distinct regions of TRPS1 can physically interact with the dynein light chain 8 protein, LC8a, that are at least 458 amino acids apart from each other. Region A covers 89 amino acids (635-723), spanning three potential C(2)H(2) zinc finger structures, and region B covers the 100 most C-terminal amino acids (1182-1281) containing the IKAROS-like motif. LC8a is known to interact with more than 10 different molecules, both proteins and nucleic acids. In most cases, LC8a was identified as a transport molecule in the cytoplasm. Interestingly, we found that LC8a co-localizes with TRPS1 in dot-like structures in the cell nucleus. In an electrophoretic mobility shift assay we could show that the interaction of LC8a and TRPS1 lowers the binding of TRPS1 to the GATA consensus sequence. In addition, GATA-regulated reporter gene assay indicated that LC8a is able to suppress the transcriptional repression activity of TRPS1.

Mutational analysis of the gene for clotting factor VIII is complicated by its large size, the high frequency of de novo mutations and its tissue-specific expression. In order to facilitate the search for mutations, we have used a combination of reverse transcription-polymerase chain reaction (RT-PCR) of ectopic factor VIII transcripts, PCR of genomic DNA, single-strand conformation polymorphism analysis and direct sequencing. Here we describe the characterization of seven potentially pathogenic mutations: five of them are novel and the reason for the pathogenicity of the sixth could be determined. Here cDNA analysis revealed the absence of the first 47 bp of exon 16 in approximately 80% of the processed factor VIII mRNA, likely due to activation of a cryptic acceptor splice site within exon 16. The other novel mutations reported here include the skipping of exon 19, which predicts the removal of the corresponding 39 amino acids from the A3 domain, and four missense mutations: W14G, Y620C, W1889L, and Q2087R.

The X‐linked bleeding disorder hemophilia A is caused by mutations in the coagulation factor VIII gene. A high frequency of de novo mutations and the large size of this gene complicate the molecular diagnostic of hemophilia A. Characterization of mutations, however, may help identify amino acids or regions with essential functional or structural properties and thereby clarify the mechanism of pathogenesis. In the present study, we describe the identification of 15 mutations in the factor VIII gene, of which eight are novel. Among the patients with severe hemophilia A, two splice mutations (IVS5‐3 and IVS19‐2), a 4‐bp deletion (TACA) at codon 1215, and a missense mutation G1850V have been characterized. The missense mutations G479R, R531C, V537D, N2129S and I2190N were found for five patients with a moderate course of hemophilia A disease. A silent mutation resulting in activation of a cryptic acceptor splice site within exon 11 and four other missense mutations Y114C, R1689H, R2150H (2x), M2164V have been identified for six patients with mild hemophilia A. Hum Mutat 12:301–303, 1998.© 1998 Wiley‐Liss, Inc.

PAX2 is a member of the PAX multigene family encoding transcription factors active in specific tissues during embryogenesis. Several PAX/Pax genes (PAX and Pax describe homologous genes in human and mice, respectively) have been shown to possess critical morphogenetic functions as identified by the analysis of mice targeted for Pax genes and the phenotype of patients heterozygous for PAX mutations. Mutations in PAX2 have been shown to be implicated in independent cases of renal-coloboma syndrome. Here, we report the characterisation of a new PAX2 isoform, viz. PAX2d, which arises because of the use of an alternative acceptor splice site within exon 12 of the PAX2 gene; this leads to a shift in the reading frame. A conserved coding region extended over the regular stop codon may emphasize the biological significance of this isoform.