RrmA regulates the stability of specific transcripts in response to both nitrogen source and oxidative stress

Differential regulation of transcript stability is an effective means by which an organism can modulate gene expression. A well-characterized example is glutamine signalled degradation of specific transcripts in Aspergillus nidulans. In the case of areA, which encodes a wide-domain transcription factor mediating nitrogen metabolite repression, the signal is mediated through a highly conserved region of the 3′ UTR. Utilizing this RNA sequence we isolated RrmA, an RNA recognition motif protein. Disruption of the respective gene led to loss of both glutamine signalled transcript degradation as well as nitrate signalled stabilization of niaD mRNA. However, nitrogen starvation was shown to act independently of RrmA in stabilizing certain transcripts. RrmA was also implicated in the regulation of arginine catabolism gene expression and the oxidative stress responses at the level of mRNA stability. ΔrrmA mutants are hypersensitive to oxidative stress. This phenotype correlates with destabilization of eifE and dhsA mRNA. eifE encodes eIF5A, a translation factor within which a conserved lysine is post-translationally modified to hypusine, a process requiring DhsA. Intriguingly, for specific transcripts RrmA mediates both stabilization and destabilization and the specificity of the signals transduced is transcript dependent, suggesting it acts in consort with other factors which differ between transcripts

The alc-GR system. A modified alc gene switch designed for use in plant tissue culture

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Deletion of the unique gene encoding a typical histone H1 has no apparent phenotype in Aspergillus nidulans

We have cloned the H1 histone gene (hhoA) of Aspergillus nidulans. This single-copy gene codes for a typical linker histone with one central globular domain. The open reading frame is interrupted by six introns. The position of the first intron is identical to that of introns found in some plant histones. An H1–GFP fusion shows exclusive nuclear localization, whereas chromosomal localization can be observed during condensation at mitosis. Surprisingly, the deletion of hhoA results in no obvious phenotype. The nucleosomal repeat length and susceptibility to micrococcal nuclease digestion of A. nidulans chromatin are unchanged in the deleted strain. The nucleosomal organization of a number of promoters, including in particular the strictly regulated niiA-niaD bidirectional promoter is not affected.This work was supported by EC grant BIO2-CT93-0147, the CNRS and the Université Paris Sud. M.I.M-P. has been the recipient of CE fellowship BIO-CT-94-8102 and a fellowship from the Fondation pour la Recherche Médicale. R.G. has been the recipient of CE fellowship BIO4-CT-96-5010Peer reviewe