Christopher Johnson

E-mail: john5771@umn.edu

Thesis advisor: Gary Dunny

Year entered: 2006

Degrees received:
B.S., Biology, Harvey Mudd College, Claremont, CA 1996

Thesis research:
pCF10 is a pheromone-inducible conjugative plasmid of Enterococcus faecalis. Cells bearing pCF10 can detect a heptapeptide signal secreted by potential recipient cells. This induces the expression of plasmid-encoded factors that mediate the adhesion of donor and recipient cells, form a mating pore between cells and transfer of a copy of pCF10 into the recipient. In the uninduced state, transcription from the prgQ promoter (PQ) of pCF10 is repressed by the plasmid encoded protein PrgX. This repression is incomplete and transcription occurs at a low level. These transcripts extend about 380nt, terminating at an intrinsic terminator, IRS1 (Inverted Repeat Sequence 1) and forming the Qs RNA. During induction, pheromone enters the cell and interacts directly with PrgX, alleviating repression of PQ. Under these conditions, Qs is still transcribed as are longer transcripts that encode genes functionally important for conjugation. I am working to elucidate the molecular mechanisms by which the cell decides when to extend transcription from PQ past IRS1. We hypothesize that transcription is extended past IRS1 when the nascent Qs RNA transcript adopts a competing secondary structure (an antiterminator) that precludes formation of the terminator. We further hypothesize that the decision is driven by interactions between nascent Qs transcripts and Qa, a sRNA transcribed from the Qs non-template strand.