Alternative transcription initiation sites generate two LCA1 Ca2+ -ATPase mRNA transcripts in tomato roots
1999
Navarro-Avino, J.P. | Hentzen, A.E. | Bennett, A.B.
The tomato LCAl gene encodes a Ca(2+) -ATPase and gives rise to two major mRNA transcripts and two distinct protein products of different size in tomato roots. The basis of the transcript size difference was investigated to assess whether the mRNA transcripts encoded distinct protein products. Primer extension and Sl nuclease analysis identified two transcription initiation sites at -72 and -1392 from the start of translation. RNA gel blot analysis of poly(A)(+) RNA isolated from phosphate-starved tomato roots using probes designed to domains of the 5'-untranslated region (UTR) or the full-length LCAl cDNA identified mRNAs of 4.7 and 3.6 kb, corresponding to mRNA originating from transcription initiation sites -1392 and -72, respectively. Screening of a cDNA library derived from phosphate-starved tomato roots yielded three cDNA clones, LCAlA, LCAlB and LCAlC (3.6, 4.5 and 5.1 kb respectively). These cDNAs contain full-length LCAl mRNA sequence derived from each transcription initiation site, with LCAlC additionally containing an intron of 0.6 kb. Sequence analysis indicated 100% identity between the three size classes of cDNA clones except for the differential 5'-UTR and the unspliced intron. Overall, the results indicate that the two major LCAl mRNA transcripts are derived by differential transcription initiation and that two of the mRNAs may encode identical protein products, while a third mRNA may correspond to a non-functional truncated protein.
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