Conserved functions of Arabidopsis mitochondrial late-acting maturation factors in the trafficking of iron‑sulfur clusters

Numerous proteins require iron?sulfur (Fe-S) clusters as cofactors for their function. Their biogenesis is a multi-step process occurring in the cytosol and mitochondria of all eukaryotes and additionally in plastids of photosynthetic eukaryotes. A basic model of Fe-S protein maturation in mitochondria has been obtained based on studies achieved in mammals and yeast, yet some molecular details, especially of the late steps, still require investigation. In particular, the late-acting biogenesis factors in plant mitochondria are poorly understood. In this study, we expressed the factors belonging to NFU, BOLA, SUFA/ISCA and IBA57 families in the respective yeast mutant strains. Expression of the Arabidopsis mitochondrial orthologs was usually sufficient to rescue the growth defects observed on specific media and/or to restore the abundance or activity of the defective Fe-S or lipoic acid-dependent enzymes. These data demonstrate that the plant mitochondrial counterparts, including duplicated isoforms, likely retained their ancestral functions. In contrast, the SUFA1 and IBA57.2 plastidial isoforms cannot rescue the lysine and glutamate auxotrophies of the respective isa1-isa2Δ and iba57Δ strains or of the isa1-isa2-iba57Δ triple mutant when expressed in combination. This suggests a specialization of the yeast mitochondrial and plant plastidial factors in these late steps of Fe-S protein biogenesis, possibly reflecting substrate-specific interactions in these different compartments.     

Analysis of the HMGI nuclear proteins in mouse neoplastic cells induced by different procedures

Four malignant tumors induced in mouse by different experimental procedures were compared as regards their high-mobility-group (HMG) proteins. All tumors showed the complete set of three HMG proteins which we call HMGI-C, I-D, and I-E. The presence of the three HMGI proteins is a characteristic of the transformed phenotype regardless of whether the tumor was chemically, virally, or spontaneously derived. However, the level of expression of the HMGI proteins is not constant in the four tumors. Using reverse-phase HPLC, the individual HMGI proteins were isolated from the spontaneously derived tumor (Lewis lung carcinoma) and shown by amino acid analysis to be similar to those previously obtained from a tumor grown in nude mice by inoculation of in vitro-transformed cells.