Novikova, O. | Search bioRxiv

bioRxiv2019

Transposon-mediated telomere destabilization: a driver of genome evolution in the blast fungus

Magnaporthe oryzae is a filamentous ascomycete fungus that causes devastating diseases of crops that include rice and wheat, and a variety of turf, forage and wild grasses. Strains from ryegrasses possess highly stable chromosome ends that undergo frequent rearrangements during vegetative growth in culture and in planta. Instability is associated with the presence of two related retrotransposons (Magnaporthe oryzae Telomeric Retrotransposons - MoTeRs) inserted within the telomere repeat tracts. The objective of the present study was to determine the mechanisms by which MoTeRs promote telomere instability. Targeted cloning, restriction mapping, and sequencing of both parental and novel telomeric restriction fragments, along with MinION sequencing of DNA from three single-spore cultures, allowed us to document the molecular alterations for 109 newly-formed telomeres. Rearrangement events included truncations of subterminal rDNA sequences; acquisition of MoTeR insertions by "plain" telomeres; insertion of the MAGGY retrotransposons into MoTeR arrays; expansion and contraction of subtelomeric tandem repeats; MoTeR truncations; duplication and terminalization of internal sequences; and breakage at long, interstitial telomeres generated during MoTeR insertion. Together, our data show that when MoTeRs invade the telomeres, they can dramatically perturb the integrity of chromosome ends, leading to the generation of unprotected DNA termini whose repair has the potential to generate chromosome alterations that extend well into the genome interior.

genomics↗

bioRxiv2018

Spliceosomal Prp8 intein at the crossroads of protein and RNA splicing

The spliceosome is a large ribonucleoprotein complex that removes introns from pre-mRNAs. At its functional core lies the essential Prp8 protein. Across diverse eukaryotes, this protein cofactor of RNA catalysis harbors a self-splicing element, called an intein. Inteins in Prp8 are extremely pervasive and are found at seven different sites in various species. Here, we focus on the Prp8 intein from Cryptococcus neoformans, a human fungal pathogen. We solved the crystal structure of this intein, revealing structural homology among self-splicing sequences in eukaryotes, including Hedgehog protein. Working with the C. neoformans Prp8 intein in a reporter assay, we find that the biologically relevant divalent metals copper and zinc inhibit intein splicing, albeit by two different mechanisms. Copper likely stimulates reversible modifications on a catalytically important cysteine, whereas zinc binds via the same critical cysteine with a Kd of ~1 nM. An intein-containing Prp8 precursor model is presented, suggesting that metal-induced protein splicing inhibition would disturb function of both Prp8 and the spliceosome. These results indicate that Prp8 protein splicing can be modulated, and that this could alter spliceosome function and RNA splicing under specific conditions.

biochemistry↗