Convergent transcription units and their promoters at both ends of pot2, an inverted repeat transposon from the rice blast fungus.

The rice blast fungus Pot2 is an inverted repeat transposon which shares structural features with the Tc1-mariner superfamily. In a search for the transposition regulatory mechanism of presently quiescent Pot2, we found truncated transcripts for the sense and antisense strands of the transposase (TPase) gene. Reverse transcription-PCR analysis identified the convergent overlapping transcription units that contain the entire coding region of the TPase gene. DNA fragments carrying presumed TATA box motifs at both ends of Pot2 proved to be functional as promoters in transient expression assays. Using these promoters on transformation vectors, stable transformants of the fungus were obtained at a frequency comparable to that with the established system. Furthermore, the antisense promoter transcribed a marker gene from one of the original sites on the chromosome. The above results indicate that the antisense RNA is transcribed by the antisense promoter at the 3' end of the element, which has implications for a possible regulatory mechanism. This is the first example of the identification of an antisense promoter within a class II transposon from a eukaryote.