Saccharomyces cerevisiae Mod5p-II contains sequences antagonistic for nuclear and cytosolic locations.
MOD5 encodes a tRNA modification activity located in three subcellular compartments. Alternative translation initiation generates Mod5p-I, located in the mitochondria and the cytosol, and Mod5p-II, located in the cytosol and nucleus. Here we study the nucleus/cytosol distribution of overexpressed Mod5p-II. Nuclear Mod5p-II appears concentrated in the nucleolus, perhaps indicating that the nuclear pool may have a different biological role than the cytoplasmic and mitochondrial pools. Mod5p contains three motifs resembling bipartite-like nuclear localization sequences (NLSs), but only one is sufficient to locate a passenger protein to the nucleus. Mutations of basic residues of this motif cumulatively contribute to a cytosolic location for the fusion proteins. These alterations also cause decreased nuclear pools of endogenous Mod5p-II. Depletion of nuclear Mod5p-II does not affect tRNATyr function. Despite the NLS, most Mod5p is cytosolic. We assessed whether Mod5p sequences cause a karyophilic reporter to be located in the cytosol. By this assay, Mod5p may contain more than one region that functions as cytoplasmic retention and/or nuclear export sequences. Thus, distribution of Mod5p results from the presence/absence of mitochondrial targeting information and sequences antagonistic for nuclear and cytosolic locations. Mod5p is highly conserved; sequences responsible for subcellular distribution appear to reside in "accessory" motifs missing from prokaryotic counterparts.
Tolerico
L H
LH
Program in Cell and Molecular Biology, Pennsylvania State University College of Medicine, Hershey, Pennsylvania 17033, USA.
Benko
A L
AL
Aris
J P
JP
Stanford
D R
DR
Martin
N C
NC
Hopper
A K
AK
D019883:Alkyl and Aryl Transferases; D000595:Amino Acid Sequence; D000818:Animals; D001692:Biological Transport; D002467:Cell Nucleus / Q000201:enzymology; D003593:Cytoplasm; D003600:Cytosol / Q000201:enzymology; D006801:Humans; D007527:Isoenzymes / Q000032:analysis* / Q000235:genetics; D008969:Molecular Sequence Data; D019913:Nuclear Localization Signals; D011506:Proteins / Q000032:analysis* / Q000235:genetics; D012441:Saccharomyces cerevisiae / Q000201:enzymology* / Q000235:genetics; D029701:Saccharomyces cerevisiae Proteins; D013347:Subcellular Fractions
D007527:Isoenzymes; D019913:Nuclear Localization Signals; D011506:Proteins; D029701:Saccharomyces cerevisiae Proteins; D019883:Alkyl and Aryl Transferases; C068392:MOD5 protein, S cerevisiae