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Low level Tc1 transposition and Tc1-induced mutations in dpy-5 Babity, Joseph M.


The transposable element Tcl is the most thoroughly studied transposon in the nematode Caenorhabditiselegans. In this thesis I have examined Tcl transposition in the Bristol strain of C. elegans and analyzed Tcl-induced mutations in the dpy-5 gene of chromosome I. In the Bristol strain of C. elegans, germline Tcl transposition has been undetectable; however, Bristol isolates were identified in which low-level Tcl transposition was observed. In the gene identified as dpy-5, one of many genes that affect overall worm morphology in C. elegans, Tcl-inducedmutations were examined and used to clone the dpy-5 gene and a second gene in the dpy-5 region. A novel Tcl element from a Bristol isolate was cloned and the genomic insertion site was analyzed. The sequence of the insertion site was found to be similar to the consensus sequence for transposition insertion indicating that germline Tcl transposition had occurred. Further analysis identified a derivative Bristol strain in which a high level of germline Tcl transposition was observed. Six Tcl-induced alleles of dpy-5 were studied. From one of these alleles a novel 2.7 kilobase pair Tcl-hybridizing EcoRI fragment was isolated and used as a tag in cloning the dpy-5 gene. Examination of Tcl-induced mutations of dpy-5 and wild type revertants revealed that the mutation was the result of Tcl transposition into a1.1 kilobase pair genomic EcoRI fragment. The dpy-5 gene was sequenced and shown to encode a 254 amino acid protein. The gene has no known homologues or protein patterns; however, a potential secretion signal peptide has been identified. Northern analysis indicates that the gene is developmentally expressed, correlating well with the onset of the Dpy-5 phenotype. Analysis of DNA sequences upstream from the dpy-5 gene reveals the presence of a neighbouring gene with homology to casein kinase I.

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