The mitochondrial DNA (mtDNA) of the chytridiomycete fungus Allomyces macrogynus is
unusually G+C rich, in intergenic (49%) versus protein coding regions (32%). These
intergenic regions comprise 26-79 bases long G+C-rich sequence elements that can be folded
into distinctive structures, consisting of two stem-loops. We found a total of 65 similar
structural elements in the A. macrogynus mtDNA, of which 39 are inserted in intergenic
regions, 20 in introns and 6 in variable regions of the rRNA genes. Some of these hairpin
structures are embedded in others, as twins or even multiples. When comparing the most
similar elements, more sequence variation is found in loops than in helical regions, and the
latter contain compensatory base changes in base-paired regions, suggesting that the particular
secondary structure of the element has a yet unidentified, important function. We have
sequenced a region comprising the carboxy-terminal of nad5, atp6 and the amino-terminal
portion of cox1 from another Allomyces species, A arbusculus, comprising 7 of these double
hairpin structural elements (DHE). Five DHE are inserted at the same position as in A.
macrogynus, while two others appear in new locations and are identical in primary sequence
to elements in A. macrogynus. The distribution pattern of DHE in A. macrogynus and between
the two related species of Allomyces suggests that deletion and transposition of these elements
occur at a high frequency. We propose that the conserved structure of DHE play a role in
their mobility.
For more information: not yet available, publication submitted.