In Saccharomyces cerevisiae, one of two cytosolic lysine-tRNAs is partially imported into mitochondria. We demonstrate that three components of the ubiquitin/26S proteasome system (UPS), Rpn13p, Rpn8p and Doa1p interact with the imported tRNA and with the essential factor of its mitochondrial targeting, pre-Msk1p. Genetic and biochemical assays demonstrate that UPS plays a dual regulatory role, since the overall inhibition of cellular proteasome activity reduces tRNA import, while specific depletion of Rpn13p or Doa1p increases it. This result suggests a functional link between UPS and tRNA mitochondrial import in yeast and indicates on the existence of negative and positive import regulators.

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Synthesis of 6(E)-and 6(Z)-(3-Ethoxycarbonylpropyl)oximes of 16α,17α-Cyclohexanopregn-4-ene-3,6,20-trione and Study of Their Interaction with Proteins of the Rat Uterine Cytosol and Blood Serum.-The suitability of steroids (VII) and (VIII) as ligands in affinity chromatography for the isolation of proteins is investigated by studying their ability to bind to proteins from the rat uterine cytosol and blood serum using competitive analysis. The more efficient binding is shown by (E)-isomer (VII), due to the fact that in (VII), the conjugated ketone in ring A is more spatially accessible for the reaction with the protein.-(LEVINA, I. S.; KULIKOVA, L. E.; KAMERNITSKII, A. V.; SHASHKOV, A. S.; SMIRNOV, A. N.; POKROVSKAYA, E. V.; Russ.