Biochem. J. (2001) 353
(403–409) (Printed in Great Britain)
Characterization of monocot and dicot plant S-adenosyl-L-methionine decarboxylase gene families including identification in the mRNA of a highly conserved pair of upstream overlapping open reading frames
Marina FRANCESCHETTI*1, Colin HANFREY*, Sonia SCARAMAGLI*1, Patrizia TORRIGIANI†, Nello BAGNI†, Daniel BURTIN*2 and Anthony J. MICHAEL*3
*Division of Food Safety Science, Institute of Food Research, Norwich Research Park, Colney, Norwich NR4 7UA, U.K., and †Dipartimento di Biologia e.s., Università di Bologna, Via Irnerio 42, 40126 Bologna, Italy
S-Adenosyl-L-methionine decarboxylase (AdoMetDC; EC 4.1.1.50) is one of the key regulatory enzymes in the biosynthesis of polyamines. Isolation of genomic and cDNA sequences from rice and Arabidopsis had indicated that this enzyme is encoded by a small multigene family in monocot and dicot plants. Analysis of rice, maize and Arabidopsis AdoMetDC cDNA species revealed that the monocot enzyme possesses an extended C-terminus relative to dicot and human enzymes. Interestingly, we discovered that all expressed plant AdoMetDC mRNA 5´ leader sequences contain a highly conserved pair of overlapping upstream open reading frames (uORFs) that overlap by one base. The 5´ tiny uORF consists of two or three codons and the 3´ small uORF encodes 50–54 residues. Sequences of the small uORFs are highly conserved between monocot, dicot and gymnosperm AdoMetDC mRNA species and the C-terminus of the plant small uORFs is conserved with the C-terminus of nematode AdoMetDC uORFs; such a conserved arrangement is strongly suggestive of a translational regulatory mechanism. No introns were found in the main AdoMetDC proenzyme ORF from any of the plant genes encoding AdoMetDC, whereas introns were found in conserved positions flanking the overlapping uORFs. The absence of the furthest 3´ intron from the Arabidopsis gene encoding AdoMetDC2 suggests that this intron was lost recently. Reverse-transcriptase-mediated PCR analysis of the two Arabidopsis genes for AdoMetDC indicated that AdoMetDC1 is abundant and ubiquitous, whereas the gene for AdoMetDC2 is expressed preferentially in leaves and inflorescences. Investigation of recently released Arabidopsis genome sequences has revealed that in addition to the two genes encoding AdoMetDC isolated as part of the present work, four additional genes are present in Arabidopsis but they are probably not expressed.
Key words: polyamine, translational regulation.
Abbreviations used: AdoMetDC, S-Adenosyl-L-methionine decarboxylase (EC 4.1.1.50); BAC, bacterial artificial chromosome; EST, expressed sequence tag; ORF, open reading frame; uORF, upstream ORF; RT–PCR, reverse-transcriptase-mediated PCR.
1Present address: Dipartimento di Biologia e.s., Universitá di Bologna, Via Irnerio 42, 40126 Bologna, Italy.
2Present address: John Innes Centre, Norwich Research Park, Colney, Norwich NR4 7UH, U.K.
3To whom correspondence should be addressed (e-mail tony.michael@bbsrc.ac.uk).
The nucleotide sequence data reported will appear in DDBJ, EMBL and GenBank Nucleotide Sequence Databases under the accession numbers Y07766, AJ251899, Y07767, AJ251915, AJ252214, AJ252213, Y07765 and AJ252212.
Received 10 July 2000/18 September 2000; accepted 7 November 2000
The Biochemical Society, London ©
2001
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