Cryptons: a group of tyrosine-recombinase-encoding DNA transposons from pathogenic fungi

Abstract

A new group of transposable elements, which the authors have named cryptons, was detected in several pathogenic fungi, including the basidiomyceteCryptococcus neoformans, and the ascomycetesCoccidioides posadasiiandHistoplasma capsulatum. These elements are unlike any previously described transposons. An archetypal member of the group, cryptonCn1, is 4 kb in length and is present at a low but variable copy number in a variety ofC. neoformansstrains. It displays interstrain variations in its insertion sites, suggesting recent mobility. The internal region contains a long gene, interrupted by several introns. The product of this gene contains a putative tyrosine recombinase near its middle, and a region similar in sequence to the DNA-binding domains of several fungal transcription factors near its C-terminus. The element contains no long repeat sequences, but is bordered by short direct repeats which may have been produced by its insertion into the host genome by recombination. Many of the structural features of cryptonCn1are conserved in the other known cryptons, suggesting that these elements represent the functional forms. The presence of cryptons in ascomycetes and basidiomycetes suggests that this is an ancient group of elements (>400 million years old). Sequence comparisons suggest that cryptons may be related to the DIRS1 andNgaro1groups of tyrosine-recombinase-encoding retrotransposons.