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 Dr. Josť de Ondarza 

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G-proteins in Paramecium tetraurelia

A. General Description

I am researching the role of G-proteins in chemosensation of Paramecium tetraurelia, a fresh-water ciliate organism. In particular, this project will entail PCR-based screening of genomic DNA for the G-protein subunit genes, protein biochemistry to isolate and characterize G-protein subunits, and behavioral assays to evaluate the role these G-proteins play in Paramecium’s ability to sense and respond to chemicals in its environment.

B. Detailed Project Descriptions

Project #1. Effect of Cholera Toxin (CTx) and Pertussis Toxin (PTx) on Paramecium tetraurelia Response to Chemoattractants.P. tetraurelia is attracted to weak solutions of acetate, glutamate, folate, biotin, cAMP, and ammonium, a response that is quantifiable by simple behavioral assays called T-mazes. (Likewise, chemorepulsion to GTP and lysozyme can be measured as well). An unresolved question in this area is whether the response to any of the receptor-mediated attractants or repellants involves G-proteins. PTx and CTx are toxins which chemically modify the alpha subunits of heterotrimeric G-proteins, thus disrupting their transduction pathway. A significant change in the response to a chemoattractant/repellant by toxin-incubated Paramecium cells would confirm the hypothesis that the integral membrane receptor-mediated chemoattraction/repulsion pathways involve heterotrimeric G-proteins.

# of students: 2 or more

Skills to be learned: 

Project #2. PCR-based cloning of the genes encoding the alpha, beta, and gamma subunits of heterotrimeric G-proteins in Paramecium tetraurelia.While the presence of G-proteins in Paramecium tetraurelia does not prove their involvement in chemosensation, it is nevertheless important to demonstrate that they do exist. Heterotrimeric G-protein genes have been cloned in many micro-organisms, from yeast to slime molds, but only partial DNA sequences are known for G-proteins in the ciliate phylum, and none in Paramecium. Preliminary data from protein isolation studies suggest the presence of several different alpha subunits in Paramecium. PCR primers have been designed from conserved amino acid sequences of all three G-protein subunits, but initial PCR screening experiments have been unsuccessful in isolating these genes. A procedure of nested PCR will now be used to confirm the hypothesis that heterotrimeric G-protein genes are present in Paramecium tetraurelia, and to clone and sequence these genes.

# of students: 2 or more

Skills to be learned: Preparation of culture media and buffers
General laboratory skills
Culturing and handling Paramecium
Data handling and statistical calculations
Agarose gel electrophoresis
DNA sequencing software

C. Interested?

Please contact me by email ( or phone (564-5156).


This page was last updated on 03/06/03 .

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