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.
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.
Dinkins
Randy D
RD
USDA-ARS Forage-Animal Production Research Unit, N220C Agriculture Science Center, North, University of Kentucky, Lexington, KY 40546-0091, USA.
Majee
Susmita Maitra
SM
Nayak
Nihar R
NR
Martin
David
D
Xu
Qilong
Q
Belcastro
Marisa P
MP
Houtz
Robert L
RL
Beach
Carol M
CM
Downie
A Bruce
AB
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
D022821:RNA Splice Sites; D026601:Protein D-Aspartate-L-Isoaspartate Methyltransferase