Biomedical subjects

Frank Narendja

Publications and source records attributed to Frank Narendja.

3 recordsLinked to original sources

PubMed2006

The GATA factor AreA regulates localization and in vivo binding site occupancy of the nitrate activator NirA.

The GATA factor AreA is a wide-domain regulator in Aspergillus nidulans with transcriptional activation and chromatin remodelling functions. AreA interacts with the nitrate-specific Zn(2)-C(6) cluster protein NirA and both proteins cooperate to synergistically activate nitrate-responsive genes. We have previously established that NirA in vivo DNA binding site occupancy is AreA dependent and in this report we provide a mechanistic explanation for our previous findings. We now show that AreA regulates NirA at two levels: (i) through the regulation of nitrate transporters, AreA affects indirectly the subcellular distribution of NirA which rapidly accumulates in the nucleus following induction; (ii) AreA directly stimulates NirA in vivo target DNA occupancy and does not act indirectly by chromatin remodelling. Simultaneous overexpression of NirA and the nitrate transporter CrnA bypasses the AreA requirement for NirA binding, permits utilization of nitrate and nitrite as sole N-sources in an areA null strain and leads to an AreA-independent nucleosome loss of positioning.

Aspergillus nidulans↗

PubMed2006

Opposing signals differentially regulate transcript stability in Aspergillus nidulans.

A good model for gene regulation, requiring the organism to monitor a complex and changing environment and respond in a precise and rapid way, is nitrogen metabolism in Aspergillus nidulans. This involves co-ordinated expression of hundreds of genes, many dependent on the transcription factor AreA, which monitors the nitrogen state of the cell. AreA activity is in part modulated by differential degradation of its transcript in response to intracellular glutamine. Here we report that glutamine triggers synchronized degradation of a large subset of transcripts involved in nitrogen metabolism. Among these are all four genes involved in the assimilation of nitrate. Significantly, we show that two of these transcripts, niaD and niiA, are stabilized by intracellular nitrate, directly reinforcing transcriptional regulation. Glutamine-signalled degradation and the nitrate-dependent stabilization of the niaD transcript are effected at the level of deadenylation and are dependent on its 3' UTR. When glutamine and nitrate are both present, nitrate stabilization is predominant, ensuring that nitrate and the toxic intermediate nitrite are removed from the cell. Regulated transcript stability is therefore an integral part of the adaptive response. This represents the first example of distinct physiological signals competing to differentially regulate transcripts at the level of deadenylation.

3' Untranslated Regions↗

PubMed2002

Nitrate and the GATA factor AreA are necessary for in vivo binding of NirA, the pathway-specific transcriptional activator of Aspergillus nidulans.

In Aspergillus nidulans, the genes coding for nitrate reductase (niaD) and nitrite reductase (niiA), are transcribed divergently from a common promoter region of 1200 basepairs. We have previously characterized the relevant cis-acting elements for the two synergistically acting transcriptional activators NirA and AreA. We have further shown that AreA is constitutively bound to a central cluster of four GATA sites, and is involved in opening the chromatin structure over the promoter region thus making additional cis-acting binding sites accessible. Here we show that the asymmetric mode of NirA-DNA interaction determined in vitro is also found in vivo. Binding of the NirA transactivator is not constitutive as in other binuclear C6-Zn2+-cluster proteins but depends on nitrate induction and, additionally, on the presence of a wild-type areA allele. Dissecting the role of AreA further, we found that it is required for intracellular nitrate accumulation and therefore could indirectly exert its effect on NirA via inducer exclusion. We have tested this possibility in a strain accumulating nitrate in the absence of areA. We found that in such a strain the intracellular presence of inducer is not sufficient to promote either chromatin rearrangement or NirA binding, implying that both processes are directly dependent on AreA.

Aspergillus nidulans↗