RESUMO
A new class of ultra-long-duration (more than 10,000 seconds) γ-ray bursts has recently been suggested. They may originate in the explosion of stars with much larger radii than those producing normal long-duration γ-ray bursts or in the tidal disruption of a star. No clear supernova has yet been associated with an ultra-long-duration γ-ray burst. Here we report that a supernova (SN 2011kl) was associated with the ultra-long-duration γ-ray burst GRB 111209A, at a redshift z of 0.677. This supernova is more than three times more luminous than type Ic supernovae associated with long-duration γ-ray bursts, and its spectrum is distinctly different. The slope of the continuum resembles those of super-luminous supernovae, but extends further down into the rest-frame ultraviolet implying a low metal content. The light curve evolves much more rapidly than those of super-luminous supernovae. This combination of high luminosity and low metal-line opacity cannot be reconciled with typical type Ic supernovae, but can be reproduced by a model where extra energy is injected by a strongly magnetized neutron star (a magnetar), which has also been proposed as the explanation for super-luminous supernovae.
RESUMO
It is now accepted that long-duration gamma-ray bursts (GRBs) are produced during the collapse of a massive star. The standard 'collapsar' model predicts that a broad-lined and luminous type Ic core-collapse supernova accompanies every long-duration GRB. This association has been confirmed in observations of several nearby GRBs. Here we report that GRB 060505 (ref. 10) and GRB 060614 (ref. 11) were not accompanied by supernova emission down to limits hundreds of times fainter than the archetypal supernova SN 1998bw that accompanied GRB 980425, and fainter than any type Ic supernova ever observed. Multi-band observations of the early afterglows, as well as spectroscopy of the host galaxies, exclude the possibility of significant dust obscuration and show that the bursts originated in actively star-forming regions. The absence of a supernova to such deep limits is qualitatively different from all previous nearby long-duration GRBs and suggests a new phenomenological type of massive stellar death.
RESUMO
Many light-responsive promoters contain GATA motifs and a number of nuclear proteins have been defined that interact with these elements. Type-IV zinc-finger proteins have been extensively characterised in animals and fungi and are referred to as GATA factors by virtue of their affinity for promoter elements containing this sequence. We previously identified cDNA sequences representing four Arabidopsis thaliana type-TV zinc-finger proteins. Here we define the organisation and expression of GATA-1, GATA-2, GATA-3 and GATA-4 as well as DNA-binding characteristics of their encoded proteins. Transcripts from all four genes can be detected in all tissues examined suggesting that they are not developmentally regulated at the level of transcription. In vitro binding experiments with Escherichia coli-derived recombinant proteins were performed using motifs previously defined as targets for nuclear GATA-binding proteins. These studies reveal differences in DNA binding specificity of GATA-1 as compared to the other three proteins. In vivo protein-DNA interactions monitored by yeast one-hybrid assays reveal different binding characteristics as compared to those defined with E. coli-derived recombinant protein. Trans-activation of gene expression by the four Arabidopsis proteins via some, but not all, DNA elements tested indicates that the Arabidopsis proteins can form functional interactions with previously defined promoter elements containing GATA motifs. We conclude that the Arabidopsis type-IV zinc-finger proteins may represent the previously defined family of nuclear GATA-binding proteins implicated in light-responsive transcription.