NUCLEOTIDE-SEQUENCE OF DDP1, A HIGH COPY NUMBER NUCLEAR PLASMID OF DICTYOSTELIUM-DISCOIDEUM

The complete nucleotide sequence of Ddp1, a high copy number 13.7-kbp endogenous nuclear plasmid of Dictyostelium discoideum is presented. P revious studies have shown nine transcripts which map to five differen t regions of Ddp1, suggesting alternative transcription initiation sit es and/or post-transcriptional processing. The sequence presented here shows five long open reading frames corresponding to previously known transcribed regions, as well as an additional reading frame, in the r egion of the presumed origin of replication. Two of the predicted prot eins from the Ddp1 reading frames have potential leader sequences and transmembrane domains, while the rest, if translated, would encode sol uble proteins. One of these has both leucine zipper and zinc finger-li ke motifs. Sequences upstream of the reading frames show strong simila rities to chromosomal promoter elements, suggesting that transcription of at least some of the plasmid-encoded genes is regulated by factors which regulate chromosomal transcription in this organism. The region containing the presumptive origin of replication contains the promote rs of the major growth-specific gene, as well as a second gene; thus, the processes of transcription and replication of Ddp1 may be intimate ly linked. The origin-encompassing region has a long homopurine/homopy rimidine stretch, which is similar to sequences shown in vitro to be c apable of forming a triple helix structure through Hoogsteen base pair ing. Possible roles for these sequences and the products of the ORFs i n plasmid maintenance are discussed. (C) 1994 Academic Press, Inc.