Abstract
BackgroundPoly(A) polymerase is a key enzyme in the machinery that mediates mRNA 3′ end formation in eukaryotes. In plants, poly(A) polymerases are encoded by modest gene families. To better understand this multiplicity of genes, poly(A) polymerase-encoding genes from several other plants, as well as from Selaginella, Physcomitrella, and Chlamydomonas, were studied.Methodology/Principal FindingsUsing bioinformatics tools, poly(A) polymerase-encoding genes were identified in the genomes of eight species in the plant lineage. Whereas Chlamydomonas reinhardtii was found to possess a single poly(A) polymerase gene, other species possessed between two and six possible poly(A) polymerase genes. With the exception of four intron-lacking genes, all of the plant poly(A) polymerase genes (but not the C. reinhardtii gene) possessed almost identical intron positions within the poly(A) polymerase coding sequences, suggesting that all plant poly(A) polymerase genes derive from a single ancestral gene. The four Arabidopsis poly(A) polymerase genes were found to be essential, based on genetic analysis of T-DNA insertion mutants. GFP fusion proteins containing three of the four Arabidopsis poly(A) polymerases localized to the nucleus, while one such fusion protein was localized in the cytoplasm. The fact that this latter protein is largely pollen-specific suggests that it has important roles in male gametogenesis.Conclusions/SignificanceOur results indicate that poly(A) polymerase genes have expanded from a single ancestral gene by a series of duplication events during the evolution of higher plants, and that individual members have undergone sorts of functional specialization so as to render them essential for plant growth and development. Perhaps the most interesting of the plant poly(A) polymerases is a novel cytoplasmic poly(A) polymerase that is expressed in pollen in Arabidopsis; this is reminiscent of spermatocyte-specific cytoplasmic poly(A) polymerases in mammals.
Highlights
Eukaryotic messenger RNAs possess characteristic 59- and 39modifications that promote the overall functionality of the molecule
Previous reports have described some properties of the Arabidopsis poly(A) polymerase gene family
Amino acid sequence alignments revealed that the greatest conservation in the various predicted proteins listed in Table 1 was
Summary
Eukaryotic messenger RNAs possess characteristic 59- and 39modifications that promote the overall functionality of the molecule. The 39 modification is an extended poly(A) tract, and serves to promote RNA stability and translatability through interactions with poly(A) binding proteins and translation initiation factors [1]. The canonical nuclear poly(A) polymerase that participates in mRNA 39 end formation is present in all eukaryotic organisms. All canonical poly(A) polymerases share a conserved N-terminal 450–500 amino acids that includes crucial RNAbinding domains, Mg-coordinating amino acid side chains, the ATP-binding active site of the enzyme, and nuclear localization signals [4,5]. 100 amino acids) and consists (in part) of additional RNA-binding domains that are important for overall function of the enzyme (e.g., [7]). Poly(A) polymerase is a key enzyme in the machinery that mediates mRNA 39 end formation in eukaryotes. To better understand this multiplicity of genes, poly(A) polymerase-encoding genes from several other plants, as well as from Selaginella, Physcomitrella, and Chlamydomonas, were studied
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