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Title: A TRANSCRIPTIONAL PROMOTER IS POSITIONED IMMEDIATELY 3' TO TRNFM IN SORGHUM MITOCHONDRIA

Author
item YAN, B - UNIVERSITY OF FLORIDA
item SALAZAR, R - UNIVERSITY OF FLORIDA
item Pring, Daryl

Submitted to: Plant Molecular Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/22/1997
Publication Date: N/A
Citation: N/A

Interpretive Summary: We have been studying gene expression in the mitochondria of sorghum. The mitochondrion is a major source of energy for the growing plant. An important part of the energy-producing system is the ability to produce high energy phosphate compounds, and a chemical named ATP is critical in these processes. A gene named atp9 is part of the process to synthesize ATP. We studied the expression of this gene and found an unusual situation wherein the gene messenger RNA (mRNA) is produced through two mechanisms. One mechanism, mRNA synthesis initiated by what is called a promoter DNA sequence, is typical and expected for a gene. The second mechanism results in a mRNA that is produced by another gene located in front of atp9 and expression of this gene releases mRNA of atp9. What is unusual is that these two processes occur at the same site. Studies of gene expression will allow manipulating regulation of genes through altering the promoter, such as found for atp9. However, even if we engineer the regulation of expression of atp9 through its promoter, the gene will still be expressed through the second mechanism. Positioning of these two mechanisms in the same location has not been documented previously and these must be considered in situations where the regulation of important genes is being studied.

Technical Abstract: Sorghum mitochondrial atp9 is substantially polymorphic among cytoplasms, with three hybridization patterns among five male sterile cytoplasms, each distinct from that of a normal, male-fertile cytoplasm. Each cytoplasm, however, is characterized by a major 650 nt transcript, regardless of male fertility status. Sequencing of flanking regions revealed that atp9 is positioned 323 bp 3' to trnfM. Primer extension revealed multiple atp9 5' transcript termini, distributed from +1 to +28 bp 3' to trnfM, with four major termini at +6, 9, 10 and 13 bp. The transcript termini could be phosphorylated with polynucleotide kinase, suggesting that they result from endonuclease activities associated with the excision of trnfM. However, guanylyl transferase and ribonuclease protection assays showed that four termini had di- or tri-phosphate, cappable termini. A consensus YRTA (TGTA) is located at 17 bp 3' to trnfM, which may function as a promoter. The juxtaposition of this putative promoter 3' to trnfM results in an atp9 transcript complex consisting of primary transcripts and transcripts resulting from the excision of trnfM.