Animal and fungal cells (in contrast to prokaryotes) contain two distinct sets of related aminoacyl-tRNA synthetases (aaRSs) encoded by nuclear genes and functioning in cytosol and mitochondria. The structural differences between mitochondrial and cytoplasmic enzymes may reflect the functional adaptation to fulfil mitochondrial processes in addition to protein synthesis. Mitochondrial import of nuclear-encoded tRNAs has been described in yeast, plants and protozoans but it has not been observed in mammalian cells. Its established that mitochondrial lysyl-tRNA synthetase (MSK) plays a prominent role in the transport of tRNA into yeast mitochondria for complementation of mitochondrial tRNAs genes mutations. We tried to identify MSK homologues in mammalian cells with the help of monospecific antibodies against pre-MSK by ELISA and Western-blot analysis. We have identified cross-reactive proteins in mitochondrial and cytoplasmic fractions of mammalian cell lysates. These data, together with the results of crossaminoacylation on mitochondrial and cytoplasmic tRNAs, suggest the presence of common antigenic determinants in the mitochondrial and cytoplasmic lysyl-tRNA synthetases from higher animals. ©L. h.

The data concerning DNA-Topoisomerase I (Topo-I) from human placenta as an autoantigen at the thyroid cancer are presented. A new effective scheme of the Topo-I purification using the High-Trap columns is described, as well as the enzyme physico-chemical properties and its immunoreactivity in the ELISA and immunoblotting. It was shown that 46 % of the sera from patients suffering the thyroid cancer were immunoreactive against Topo-I, 36 % of autoantibodies from thyroid cancer patients sera recognized sequential determinants on the Topo-I molecule. The highest levels of immunoreacivity were observed in the sera of thyroid cancer patients accompanied by autoimmune thyroiditis. We suggest a possible linkage between the autoimmune processes and malignization of the thyroid gland cells.

No abstract