Sequence organization and gene expression of pGD1, a plasmid found in a wild isolate of Dictyostelium

We have determined the complete nucleotide sequence of pDG1, a plasmid found in a wild isolate of Dictyostelium. The 4439-bp long pDG1 contains only one, 2718-bases-long, open reading frame (ORF) and nearly perfect inverted repeats of 551 bp and 552 bp. Northern-blot analysis showed that only one 2.7-kb poly (A)+ RNA transcript was expressed at a maximum level, 2 h (early aggregation stage) after the onset of development. The expression of this transcript was suppressed by the addition of cAMP. In the upstream region of the ORF, there are several putative consensus sequences, e.g. (1) TGACTTAGAA-AAATT which is a putative site for cleavage by topoisomerase I, and (2) TGACGACA which may be a cAMP-responsive element, found in several genes that are regulated by cAMP at the level of transcription. A possible mechanism of the partitioning of pDG1 into daughter cells is discussed.