title: Changing transcriptional initiation sites and alternative 5'- and 3'-splice site selection of the first intron deploys Arabidopsis protein isoaspartyl methyltransferase2 variants to different subcellular compartments.
abstract: Arabidopsis thaliana (L.) Heynh. possesses two PROTEIN-L-ISOASPARTATE METHYLTRANSFERASE (PIMT) genes encoding enzymes (EC 2.1.1.77) capable of converting uncoded l-isoaspartyl residues, arising spontaneously at l-asparaginyl and l-aspartyl sites in proteins, to l-aspartate. PIMT2 produces at least eight transcripts by using four transcriptional initiation sites (TIS; resulting in three different initiating methionines) and both 5'- and 3'-alternative splice site selection of the first intron. The transcripts produce mature proteins capable of converting l-isoaspartate to l-aspartate in small peptide substrates. PIMT:GFP fusion proteins generated a detectable signal in the nucleus. However, whether the protein was also detectable in the cytoplasm, endo-membrane system, chloroplasts, and/or mitochondria, depended on the transcript from which it was produced. On-blot-methylation of proteins, prior to the completion of germination, indicated that cruciferin subunits contain isoaspartate. The implications of using transcriptional mechanisms to expand a single gene's repertoire to protein variants capable of entry into the cell's various compartments are discussed in light of PIMT's presumed role in repairing the proteome.
authors.affiliation: USDA-ARS Forage-Animal Production Research Unit, N220C Agriculture Science Center, North, University of Kentucky, Lexington, KY 40546-0091, USA.
authors.forename: Randy D
authors.initials: RD
authors.lastname: Dinkins
authors.forename: Susmita Maitra
authors.initials: SM
authors.lastname: Majee
authors.forename: Nihar R
authors.initials: NR
authors.lastname: Nayak
authors.forename: David
authors.initials: D
authors.lastname: Martin
authors.forename: Qilong
authors.initials: Q
authors.lastname: Xu
authors.forename: Marisa P
authors.initials: MP
authors.lastname: Belcastro
authors.forename: Robert L
authors.initials: RL
authors.lastname: Houtz
authors.forename: Carol M
authors.initials: CM
authors.lastname: Beach
authors.forename: A Bruce
authors.initials: AB
authors.lastname: Downie
mesh_terms: D017398:Alternative Splicing; D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000201:enzymology* / Q000235:genetics; D001483:Base Sequence; D015180:Electrophoresis, Gel, Two-Dimensional; D007438:Introns; D008745:Methylation; D008969:Molecular Sequence Data; D026601:Protein D-Aspartate-L-Isoaspartate Methyltransferase / Q000235:genetics / Q000378:metabolism*; D022821:RNA Splice Sites; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D013347:Subcellular Fractions / Q000201:enzymology; D024363:Transcription Initiation Site
chemical_list: D022821:RNA Splice Sites; D026601:Protein D-Aspartate-L-Isoaspartate Methyltransferase