A polymorphic bipartite motif signals nuclear targeting of early auxin-inducible proteins related to PS-IAA4 from pea (Pisum sativum).
The plant hormone, indoleacetic acid (IAA), transcriptionally activates two early genes in pea, PS-IAA4/5 and PS-IAA6 that encode short-lived nuclear proteins. The identification of the nuclear localization signals (NLS) in PS-IAA4 and PS-IAA6 using progressive deletion analysis and site-directed mutagenesis is reported. A C-terminal SV40-type NLS is sufficient to direct the beta-glucuronidase reporter to the nucleus of transiently transformed tobacco protoplasts, but is dispensible for nuclear localization of both proteins. The dominant and essential NLS in PS-IAA4 and PS-IAA6 overlap with a bipartite basic motif which is polymorphic and conserved in related proteins from other plant species, having the consensus sequence (KKNEK)KR-X(24-71)-(RSXRK)/(RK/RK). Both basic elements of this motif in PS-IAA4, (KR-X41-RSYRK), function interdependently as a bipartite NLS. However, in PS-IAA6 (KKNEKKR-X36-RKK) the upstream element of the corresponding motif contains additional basic residues which allow its autonomous function as an SV40-type monopartite NLS. The spacer-length polymorphism, X(24-70), in respective bipartite NLS peptides of several PS-IAA4-like proteins from Arabidopsis thaliana does not affect nuclear targeting function. The structural and functional variation of the bipartite basic motif in PS-IAA4-like proteins supports the proposed integrated consensus of NLS.
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Plant Gene Expression Center, Albany, CA 94710, USA.
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D000595:Amino Acid Sequence; D002467:Cell Nucleus / Q000378:metabolism*; D007210:Indoleacetic Acids / Q000378:metabolism* / Q000502:physiology*; D008969:Molecular Sequence Data; D018532:Pisum sativum / Q000378:metabolism*; D010940:Plant Proteins / Q000096:biosynthesis / Q000378:metabolism*; D017384:Sequence Deletion; D017386:Sequence Homology, Amino Acid
D007210:Indoleacetic Acids; D010940:Plant Proteins; C030737:indoleacetic acid