MAIZE MITOCHONDRIAL PLASMID S-1 SEQUENCES SHARE HOMOLOGY WITH CHLOROPLAST GENE psbA

Ronald R. Sederoff ¹, Pamela Ronald ², Patricia Bedinger ², Carol Rivin ², Virginia Walbot ², Molly Bland ³, and C. S. Levings III ³

¹ Institute of Forest Genetics, Pactific Southwest Forest and Range Experiment Station, USDA, US Forest Service, P.O. Box 245, Berkeley, California 94701
² Department of Biological Sciences, Stanford University, Stanford, California 94305
³ Department of Genetics, North Carolina State University, Raleigh, North Carolina 27695-7614

The linear, 6397-base pair (bp), mitochondrial S-1 DNA molecule from maize contains a 420-bp segment that is homologous with the chloroplast gene (psbA) that codes for the quinone binding protein of photosystem II. This is the first report of a chloroplast sequence in a naturally occurring viral-like or plasmid DNA. The complete sequence of the S-1 chloroplast segment has been compared with homologous regions of six different chloroplast genes. The S-1 segment has diverged from the other genes both by length mutation and base substitution. Several of the length mutations are exact adjacent tandem duplications of 4 and 5 bp similar to "footprints" left after excision of transposable elements in maize nuclear DNA.