Charge versus sequence for nuclear/nucleolar localization of plant ribosomal proteins.
Ribosomal subunit assembly in the nucleolus is dependent on efficient targeting of ribosomal proteins (RPs) from the cytoplasm into the nucleus and nucleolus. Nuclear/nucleolar localization of a protein is generally mediated by one or more specific stretches of basic amino acids-nuclear/nucleolar localization signals (NLSs/NoLSs). Arabidopsis thaliana RPL23aA has eight putative NLSs/NoLSs (pNLSs/NoLSs). Here we mutated all eight NLS/NoLSs individually and in groups and showed, via transient expression in tobacco cells that nucleolar localization of RPL23aA was disrupted by mutation of various combinations of five or more pNLSs/NoLSs. Mutation of all eight pNLSs/NoLSs, a 50 % reduction in total basic charge of RPL23aA, resulted in a complete disruption of nucleolar localization, however, the protein can still localize to the nucleus. As no individual or specific combination of NoLSs was absolutely required for nucleolar localization, we suggest that nucleolar localization/retention of RPL23aA is dependent on the overall basic charge. In addition to the optimal basic charge conferred by these NoLSs, nucleolar localization/retention of RPL23aA also required a C-terminal putative 26S rRNA binding site. In contrast, in the RPs RPS8A and RPL15A, mutation of just two and three N-terminal pNLSs, respectively, disrupted both nuclear and nucleolar localization of these two RPs, indicating differential signal requirements for nuclear and nucleolar localization of the three Arabidopsis RPs RPL23aA, RPL15A and RPS8A.
Department of Biology, University of Saskatchewan, Saskatoon, SK, S7N 5E2, Canada.
Raghavendra P
RP
Savada
Peta C
PC
Bonham-Smith
D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000166:cytology* / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000737:chemistry* / Q000378:metabolism*; D002466:Cell Nucleolus / Q000378:metabolism*; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics; D019913:Nuclear Localization Signals; D030821:Plants, Genetically Modified; D021381:Protein Transport; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D012269:Ribosomal Proteins / Q000737:chemistry* / Q000378:metabolism*; D013329:Structure-Activity Relationship; D014026:Nicotiana / Q000235:genetics; D014170:Transformation, Genetic
D029681:Arabidopsis Proteins; D019913:Nuclear Localization Signals; D011993:Recombinant Fusion Proteins; D012269:Ribosomal Proteins; C519026:ribosomal protein L23A, Arabidopsis