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Abstract

The putrescine N-methyltransferase (PMT) cDNA clone previously isolated from tobacco encodes a spermidine synthase-like protein with an 11 amino acid element repeated four times in tandem at the amino terminus. Genomic Southern blot analyses indicated that this N-terminal repeat array is found in tobacco PMTs but absent in Hyoscyamus and Atropa PMTs. A truncated tobacco PMT in which this repeat array was entirely removed still retained full enzymatic activity when expressed in Escherichia coli. Three PMT genes (NsPMT1, NsPMT2, NsPMT3) isolated from Nicotiana sylvestris encode two, five, and nine tandem repeats, respectively, in the first exon, but otherwise encode highly conserved proteins. Analysis of PCR fragments amplified from the genomes of N. tabacum and its two probable progenitors shows that one of the nine repeat elements in NsPMT3 was precisely deleted in the corresponding N. tabacum gene. These results indicate that direct tandem repeats of a 33 bp sequence that encodes 11 amino acids of no obvious function were added to the ancestral Nicotiana PMT gene, and that the tandem repetition was genetically very unstable, contracting or expanding during evolution of the Nicotiana species.

A Polyamine Metabolon Involving Aminopropyl Transferase Complexes in Arabidopsis

“…Soybean SPDS was reported to be a monomer of 74 kD, whereas maize SPDS was purified as a monomer of 43 kD (for review, see Yoon et al, 2000). Recently, molecular studies identified highly conserved duplicated genes in Datura , Hyoscyamus , and pea that code for closely related SDPS proteins of 36 to 39 kD (Hashimoto et al, 1998;Alabadí and Carbonell, 1999). To determine whether plant SPDS homologs are capable of interacting by forming homodimers and/or heterodimers, and to possibly identify additional protein-interacting partners, we performed a protein interaction screen using the Arabidopsis SPDS2 protein as bait in fusion with the Gal4 DNA binding domain in a yeast two-hybrid system (Durfee et al, 1993;Harper et al, 1993).…”

“…A coordinated reduction of spermidine, SAMDC, and SPDS levels during stress suggests that the regulation of SPDS activity plays an important role in the proper adjustment of plant polyamine levels (Yamanoha and Cohen, 1985;Tiburcio et al, 1993). Duplicated genes that encode two closely related and differentially regulated SPDS isologs (SPDS1 and SPDS2) have been identified in pea, Datura , and Hyoscyamus (Hashimoto et al, 1998;Alabadí and Carbonell, 1999). Three Arabidopsis SPDS-like gene sequences have been deposited in GenBank, although only one gene, AtSPDS (SPDS2), has been characterized (Hashimoto et al, 1998).…”

“…Duplicated genes that encode two closely related and differentially regulated SPDS isologs (SPDS1 and SPDS2) have been identified in pea, Datura , and Hyoscyamus (Hashimoto et al, 1998;Alabadí and Carbonell, 1999). Three Arabidopsis SPDS-like gene sequences have been deposited in GenBank, although only one gene, AtSPDS (SPDS2), has been characterized (Hashimoto et al, 1998). The SPDS orthologs from Escherichia coli , rat, bovine, and human sources are thought to be dimers (Lakanen et al, 1995).…”

Bases moleculares de la síntesis de termoespermina y sus implicaciones en el desarrollo vascular de Arabidopsis thaliana

“…En A. thaliana existen 2 genes (ADC1 y 2) que codifican esta actividad, un gen que codifica la actividad AIH (AIH) (Janowitz et al 2003) y otro la CPA (NLP1) (Piotrowski et al 2003). También existen dos genes que codifican la actividad SPDS (SPD1 y 2) (Hashimoto et al 1998) uno para la SPMS (SPM1) (Panicot et al 2002) y otro para la tSPMS (ACL5) (Knott et al 2007). Por último, la actividad SAMDC es codificada por cuatro genes distintos (SAMDC1, 2, 3 y 4) (Franceschetti et al 2001).…”

“…Incluso se ha propuesto un modelo de acción de las espermidina sintasas (Korolev et al 2002;Wu et al 2007). De todos estos trabajos se ha podido concluir que el centro activo de las aminopropil transferasas conocidas contiene una gran cantidad de residuos muy conservados (Hashimoto et al 1998).…”