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The chromatin high mobility group protein 1 (HMGB1) is a very abundant and conserved protein that is structured into two HMG box domains plus a highly acidic C-terminal domain. From the ability to bind DNA nonspecifically and to interact with various proteins, several functions in DNA-related processes have been assigned to HMGB1. Nevertheless, its functional role remains the subject of controversy. Using a phage display approach we have shown that HMGB1 can recognize several peptide motifs. A computer search of the protein data bases found peptide homologies with proteins already known to interact with HMGB1, like p53, and have allowed us to identify new potential candidates. Among them, transcriptional activators like the heterogeneous nuclear ribonucleoprotein K (hnRNP K), repressors like methyl-CpG binding protein 2 (MeCP2), and co-repressors like the retinoblastoma susceptibility protein (pRb) and Groucho-related gene proteins 1 (Grg1) and 5 (Grg5) can be found. A detailed analysis of the interaction of Grgl with HMGB1 confirmed that the binding region contained the sequence homologous to one of the peptides identified. Our results have led us to propose that HMGB1 may play a central role in the stabilization and/or assembly of several multifunctional complexes through protein-protein interactions. ; This work was supported by a European Union Grant FMRX-CT97-0109 and Comissió Interdepartamental de Recerca i Innovació Tecnològica (CIRIT) of the Generalitat de Catalunya Grant SGR97-55. This work was carried out in the context of the Centre de Referència en Biotecnologia of the CIRIT of the Generalitat de Catalunya ; Peer Reviewed

GAGA factor plays important roles during Drosophila embryogenesis and its maternal contribution is essential for early development. Here, the role of GAGA factor was studied in 3rd instar larvae using depletion and overexpression conditions in wing disc and transcriptome analysis. We found that genes changing expression were different to those previously described using GAGA mutants in embryos. No apparent phenotypes on GAGA depletion could usually be observed at larval stages in imaginal discs but a strong effect on salivary gland polytene chromosomes was observed. In the adult, GAGA depletion produced many defects like abnormal cell proliferation in the wing, impaired dorsal closure and resulted in homeotic transformation of abdominal segment A5. Unexpectedly, no effects on Ultrabithorax expression were observed. Short overexpression of GAGA factor in 3rd instar larvae also resulted in activation of a set of genes not previously described to be under GAGA regulation, and in lethality at pupa. Our results suggest a little contribution of GAGA factor on gene transcription in wing discs and a change of the genes regulated in comparison with embryo. GAGA factor activity thus correlates with the global changes in gene expression that take place at the embryo-to-larva and, later, at the larva-to-pupa transitions. ; This work was supported by grants of the Ministerio de Educación y Ciencia of the Spanish Government (BFU-2007-64395/BMC), the MICINN (CSD2006-49 and BFU2009-07111) and the Generalitat de Catalunya (SGR2009-1023). M.B. was supported by I3P CPG_06_0034 contract from CSIC, and grant BFU-2007-64395/BMC contract of the Spanish Government. D.P. was supported by an FPU fellowship from the Spanish Government ; Peer Reviewed

GAGA is a nuclear protein encoded by the Trithorax-like gene in Drosophila that is expressed in at least two isoforms generated by alternative splicing. By means of its specific interaction with DNA, GAGA has been involved in several nuclear transactions including regulation of gene expression. Here we have studied the GAGA519 isoform as a transcription factor. In vitro, the transactivation domain has been assigned to the 93 C- terminal residues that correspond to a glutamine-rich domain (Q-domain). It presents an internal modular structure and acts independently of the rest of the protein. In vivo, in Drosophila SL2 cells, Q-domain can transactivate reporter genes either in the form of GAGA or Gal4BD-Q fusions, whereas a GAGA mutant deleted of the Q-domain cannot. Our results give support to the notion that GAGA can function as a transcription activating factor. ; This work was supported by Spanish Dirección General de Enzeñanza Superior Grant PB96-0812, European Union Grant FMRX-CT97-0109, and Comissió Interdepartamental de Recerca i InnovacióTecnològica (CIRIT) of the Generalitat de Catalunya Grant SGR97-55. This work was carried out in the context of the Centre de Referència en Biotecnologia of the CIRIT of the Generalitat de Catalunya ; Peer Reviewed