Are Mu-homologous sequences present in mitochondria? --Carol Leja, Susan Gabay-Laughnan and J. R. Laughnan
Several inverted and direct repeats are known to be present in the mitochondrial genome of maize. Homologous repeats may recombine with each other and, consequently, the DNA is reorganized. Cytoplasmic reversion in cms-S lines of maize is associated with loss of specific repeat sequences and/or reorganization of contiguous DNA sequences. Two experiments were performed to determine the following: (1) whether or not sequences homologous to the terminus of Mu, which may serve as additional sites for recombination, are present in the mitochondrial genome; (2) if present, do the termini indicate the presence of complete elements that could be associated with apparent loss and reappearance of mitochondrial DNA sequences, and (3) if present, do these elements account for the highly unstable nature of a WF9-RD cytoplasmic revertant.

Mitochondrial DNA from WF9-RD sterile and a corresponding cytoplasmic revertant (cyto-rev) was digested with HindIII and EcoRI. The HindIII and EcoRI digests were electrophoresed in a 1% agarose gel and blotted onto a nylon membrane. The Southern blot was probed with a clone obtained from Vicki Chandler. The clone, pDTE1, contains approximately 220 bp of the Mu terminus. No homology to the Mu terminus was detected in the mitochondrial DNA.

Mitochondrial RNA from WF9-N x M82510, WF9-RD sterile, WF9-RD cyto-rev, WF9-RD cyto-rev x M8257 (fertile) and WF9-RD cyto-rev x M8258 (sterile) was electrophoresed in a 1.2% agarose gel and blotted onto a nylon membrane. When the Northern blot was probed with pDTE1, no hybridization signal was obtained.

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