Abstract
Helitrons are eukaryotic rolling circle replication transposons. Computer-predicted autonomous Helitrons encode a putative transposase, Rep/Hel-TPase, containing a nuclease/ligase domain for the replication initiation protein and a DNA helicase domain. Plant Helitrons carry an additional gene, RPA-TPase, which is related to RPA70. Although Helitrons are found in diverse genomes, neither an autonomous element nor a transposition event has been reported.
A spontaneous pearly-s mutant of Ipomoea tricolor, exhibiting white flowers and isolated in approximately 1940, has an novel Helitron, named Hel-It1, integrated into DFR-B. Hel-It1-related elements are scattered in the Ipomoea genome, and only a fraction of the pearly-s plants was found to carry Hel-It1 at another insertion site. Hel-It1 carries the two putative transposase genes, Rep/Hel-TPase and RPA-TPase, which contain a nonsense and a frameshift mutation, respectively. The wild-type RPA-TPase transcripts are expressed in the pearly-s mutant. We will discuss mobility of Hel-It1 and a putative autonomous element.
