IMPORT OF CYTOPLASMIC LYSINE TRANSFER-RNA INTO BAKERS-YEAST MITOCHONDRIA - IN-VIVO AND IN-VITRO TEST SYSTEMS

Two model systems have been developed allowing investigation of cytopl asmic lysine tRNA targeting into the mitochondrial compartment of S. c erevisiae cells. When live yeast cells were subjected to pore-forming electric pulses in the presence of labeled tRNAs, all the nucleic acid s could be detected in the cytoplasm; however only tRNA(CUU)(Lys) was found in the mitochondrial compartment. Targeting of this tRNA into is olated mitochondria was ATP-dependent and required that two soluble pr otein fractions (high-affinity heparin-binding proteins and proteins d evoid of polyanion-binding activity) be present in the incubation medi um. The import efficiency was increased by tRNA(Lys) aminoacylation or addition of lysyl-tRNA synthase; this did not abolish the need for hi gh-affinity heparin-binding proteins. The unmodified transcripts of th e tRNA(CUU)(Lys) gene could also be imported into mitochondria.