LINEAR MITOCHONDRIAL GENOME ORGANIZATION IN-VIVO IN THE GENUS PYTHIUM

Pulsed-field gel electrophoresis (PFGE) of isolates of Pythium oligand rum with linear mitochondrial genomes revealed a distinct band in ethi dium bromide-stained gels similar in size to values estimated by restr iction mapping of mitochondrial DNA (mtDNA). Southern analysis confirm ed that these bands were mtDNA and indicated that linear genomes were present in unit-length size as well as multimers. Isolates of this spe cies with circular mtDNA restriction maps also had low levels of linea r mono- and multimers visualized by Southern analysis of PFGE gels. Ex amination of 17 additional species revealed similar results; three spe cies had distinct linear mtDNA bands in ethidium bromide-stained gels while the remainder had linear mono- and multi-mers in lower amounts d etected only by Southern analysis. Sequence analysis of an isolate of P. oligandrum with a primarily circular mitochondrial genomic map and a low amount of linear molecules revealed that the small unique region of the circular map (which corresponded to the terminal region of lin ear genomes) was flanked by palindromic intrastrand complementary sequ ences separated by a unique 194-bp sequence. Sequences with similarity to ATPase9 coding regions from other organisms were located adjacent to this region. Sequences with similarity to mitochondrial origins of replication and autonomously replicating sequences were also located i n this region: their potential involvement in the generation of linear molecules is discussed.