Identification and characterization of Npl3 as a novel prion like protein and its function in the regulation of gene expression in <em>Saccharomyces cerevisiae</em>

Abstract

Nuclear protein localization-3 (Npl3) is a highly dynamic protein involved in mRNA biogenesis. Previous studies showed that the <em>npl3-95</em> allele encodes a protein that can aggregate into high molecular weight complexes. Besides, two different bioinformatics analysis scored Npl3 as a potential prion protein in yeast. Npl3 protein was characterized as a novel prion-like protein in <em>Saccharomyces</em> cerevisiae using genetic and biochemical criteria. Results presented in this doctoral dissertation show that; (1) Npl3 harbors a putative prion domain in its RGG domain, (2) the paromomycin sensitivity phenotype associated with the <em>npl3-95</em> mutant allele is dominant and shows non-mendelian inheritance (cytoplasmic inheritance), (3) GndHCl treatment and <em>HSP104</em> deletion eliminate the paromomycin sensitivity phenotype, and (4) over-expression of the Npl3 wild type protein induces prion-like aggregates. Interestingly, the presence of the Npl3 prion-like form confers the acquisition of an adenine prototrophy phenotype and a decrease in flocculation in the yeast <em>Saccharomyces cerevisiae</em>. Altogether, the results presented in this dissertation provide new evidence of the biological significance of yeast prions and their regulatory role in gene expression.