Date of Award:

5-1-1994

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Biology

Department name when degree awarded

Biology (Molecular Biology)

Committee Chair(s)

Dennis L. Welker (Committee Chair), Gregory J. Podgorski (Committee Co-Chair)

Committee

Dennis L. Welker

Committee

Gregory J. Podgorski

Committee

Mary E. Barkworth

Committee

Jeffery R. Broadbent

Committee

Jon Y. Takemoto

Abstract

Three new Dictyostelium plasmid families were established: the Ddp1 plasmid family contains Ddp1, Dmp1, and Dmp2; the Dpp1 plasmid family contains Dpp1A, Dpp1B, and Dpp2; and the Dpp3 plasmid family contains Dpp3, Dpp4, and Dpp5. Plasmids Dpp1B, Dpp4, and Dpp5 were discovered in this work. The Ddp1 plasmid family contains two characteristic open reading frames: a G1 or G1-like open reading frame and a G5 G5-like open reading frame. These, along with an origin of replication, appear to comprise the basic replicon of the Ddp1 plasmid family. Besides the basic replicon, Ddp1 possesses four extra genes, G2/G3/D4, G4/D5, D1/D3, and D2, while Dmp1 and Dmp2 have either four (Dmp1) or three (Dmp2) copies of a 173-base pair degenerate direct repeat. The Dpp1 plasmid family is characterized by the presence of a 72-base pair inverted repeat. The Dpp3 plasmid family is characterized by the presence of a region rich in short direct repeats. The plasmids of the Dpp1 and Dpp3 plasmid families do not show extended open reading frames. A constitutively expressed transcript of 0.9 kilobase and a developmentally regulated transcript of 1.0 kilobase were detected from a 591-base pair Ddp1 open reading frame. This gene is located in the region containing the plasmid’s origin of replication. No transcripts had been detected from this open reading frame in previous studies. The product of this open reading frame (G5/D6) regulates expression of the G4/D5 gene on Ddp1 directly in a negative, trans-acting way and the G1, G2/G3/D4, and G5/D6 genes directly or indirectly. Due to its regulatory effects, the G5/D6 gene is important for both monomerization and copy number control of Ddp1. Finally, the Ddp1 origin of replication was localized to a 544-base pair fragment that contains the promoters of both the G1 and G5/D6 genes, multiple copies of a repeat element (TTTTGACT), and a polyA/polyT rich sequence. These features are similar to those of other eukaryotic replication origins.

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