Transcription of Dictyostelium discoideum Transposable Element DIRS-1

DIRS-1 is a Dictyostelium discoideum transposable element that contains heat shock promoter sequences in the inverted terminal repeats. We showed that transcription of a 4.5-kilobase polyadenylated RNA initiates at a discrete site within the left-terminal repeat of DIRS-1, downstream from heat shock promoter and TATA box sequences. This RNA represents a full-length transcript of DIRS-1. We describe a cDNA clone that contains the 4.1 kilobases of internal sequence of DIRS-1, a cDNA clone that spans the junction between the internal sequences and the right-terminal repeat, and a cDNA clone that appears to have been transcribed from a rearranged genomic copy of DIRS-1. A second DIRS-1 RNA, named E1, is transcribed on the opposite strand of DIRS-1 from the 4.5-kilobase RNA and is under control of the heat shock promoter in the right-terminal repeat. E1 transcription initiates at multiple positions both within and downstream from the right-terminal repeat. The same transcriptional initiation sites are used during normal development and during heat shock, suggesting that in all cases DIRS-1 transcription is regulated by the heat shock promoters contained within the two terminal repeats.