Abstract
In the Japanese morning glory (Ipomoea nil), several responsible genes for unstable mutations were isolated, and all transposable elements inserted in these genes belong to En/Spm (CACTA)-related element, Tpn1 family. All Tpns identified were non-autonomous elements that truncated transposase gene and captured host gene sequences. The mRNAs for transposase proteins TNPδ and TNPα are expressed by alternative splicing from autonomous Tpn as other En/Spm-related elements, and they mediate the transposition of non-autonomous elements. TNPδ has TNPD/TNP2 domains conserved in other En/Spm transposons. On the other hands, TNPα includes C-terminal sequence showing a homology to cysteine protease domain. This protease domain is also conserved in Rim2 transposon from rice and CACTA-related transposons from Medicago, but not En/Spm from maize and Tam1 from Antirrhinum, suggesting that Tpn have a different transposition mechanism.
