THE REPLICATION ORIGIN POSITION AND ITS RELATIONSHIP TO A NEGATIVE TRANS-ACTING TRANSCRIPTION REGULATOR ENCODED BY DICTYOSTELIUM-DISCOIDEUMNUCLEAR PLASMID DDP1

The replication origin of the Dictyostelium discoideum plasmid Ddp1 wa s localized to a 543-bp region. This includes most of the AT-rich inte rgenic region between the G1 and G5/D6 genes containing both of their promoters and multiple copies of a TTTTGACT repeat. The G5/D6 gene, wh ich lies adjacent to, and partially overlaps, the 543-bp origin region , encodes a trans-acting factor that negatively regulates transcriptio n of the G4/D5 gene. Inactivation of the G5/D6 gene led to expression of a transcript (G6) 0.2 kb larger than the D5 transcript from the G4/ D5 gene in vegetative and developing cells. The G5/D6 gene also regula tes transcription of the G1, G2/G3/D4 and G5/D6 genes either alone or in concert with other Ddp1 gene products.