Biomedical subjects

Tadamasa Sasaki

Publications and source records attributed to Tadamasa Sasaki.

3 recordsLinked to original sources

PubMed2006

A simple in vitro RNA editing assay for chloroplast transcripts using fluorescent dideoxynucleotides: distinct types of sequence elements required for editing of ndh transcripts.

RNA editing is found in various transcripts from land plant chloroplasts. In tobacco chloroplasts, C-to-U conversion occurs at 36 specific sites including two sites identified in this work. Our RNA editing assay system using chloroplast extracts facilitated biochemical analyses of editing reactions but required mRNAs labeled with (32)P at specific sites. Here, we have improved the in vitro system using fluorescence-labeled chain terminators, ddGTP and ddATP, and have measured the editing activity at 19 sites in ndh transcripts. Editing activities varied from site to site. It has been reported that one editing site in ndhA mRNAs is present in spinach but absent in tobacco, but a corresponding editing capacity had been found in vivo in tobacco using biolistic transformation. We confirmed biochemically the existence of this activity in tobacco extracts. Using the non-radioactive assay, we examined sequences essential for editing within a 50-nt mRNA region encompassing an editing site. Editing of the ndhB-2 site requires a short sequence in front of the editing site, while that of the ndhF mRNA requires two separate regions, a sequence surrounding the editing site and a 5' distal sequence. These results suggest that distinct editing mechanisms are present in chloroplasts.

Chloroplasts↗

PubMed2004

A systematic search for RNA editing sites in pea chloroplasts: an editing event causes diversification from the evolutionarily conserved amino acid sequence.

RNA editing in higher plant chloroplasts involves C-to-U conversion at specific sites in the transcripts. To examine whether pea shares editing sites with other angiosperms, a systematic search for editing sites in pea chloroplast transcripts was performed. Based on amino acid sequence alignment, 451 RNA editing sites were predicted from 60 transcripts. Sequence analysis of amplified cDNAs for these potential editing sites revealed 19 true editing sites from 13 transcripts. Together with those reported previously, the total number of editing sites is 27 from 16 transcripts in pea chloroplasts. Twenty-two sites are conserved among other plant species, whereas five sites are unique to pea. Among the 27 editing sites, seven are partially edited. The most interesting is the ndhG site 1, which has led to the diversification of the evolutionarily conserved amino acid sequence. This observation suggests that some of the editing events cause the diversity of amino acid sequences, and hence, that prediction of editing sites based on amino acid sequence alignment has its own limitations.

Amino Acid Sequence↗

PubMed2003

Identification of RNA editing sites in chloroplast transcripts from the maternal and paternal progenitors of tobacco (Nicotiana tabacum): comparative analysis shows the involvement of distinct trans-factors for ndhB editing.

RNA editing alters genomic nucleotide sequences at the transcript level. In higher plant chloroplasts, C-to-U conversion is known to occur at around 30 specific sites. The tobacco cultivar Nicotiana tabacum is an amphidiploid derived from ancestors of N. sylvestris (maternal) and N. tomentosiformis (paternal). The chloroplast genome of N. tabacum is believed to originate from an ancestor of N. sylvestris. To study the evolution of RNA editing in higher plant chloroplasts, editing sites in the two likely progenitors have first been identified based on those found in N. tabacum. Altogether 34, 33, and 32 editing sites have been found in the chloroplast transcripts from N. tabacum, N. sylvestris, and N. tomentosiformis, respectively. Thirty-one sites are conserved among the three species, whereas remarkable differences are observed in the editing of ndhB and ndhD transcripts. Sites 7 and 8 in ndhB mRNAs are separated only by five nt, and both are edited in N. tabacum and N. sylvestris. However, site 8 is not edited in N. tomentosiformis, indicating that distinct trans-factors are involved in the two editing events. The first site in ndhD mRNAs is edited to produce an AUG start codon in N. sylvestris as well as in N. tabacum but not in N. tomentosiformis, suggesting that a distinct mechanism operates for the translational initiation of N. tomentosiformis ndhD mRNAs. Four to six sites are edited partially in green leaves. Some of these sites may represent evolutionary intermediates in the process of losing editing events.

Cell Lineage↗