to produce a version of Sup35p which does not include the N and M regions. The Sup35p protein is 685 amino acids long. The C-terminal contains 5 complete and one incomplete repeat of the Oligopeptide repeat sequence PQGGYQQ-YN. In modified versions of the gene, it has been shown that the more repeats of this sequence present, the more the protein is to assume the [Psi+] confirmation. In fact, the addition of two extra repeats (R2) result in the [Psi-] to [Psi+] conversion in being 5000 times faster. PMN2, a mutant, dominant version of the gene Sup35p, has a glycine to aspartic acid substitution in the second repeat. The resulting phenotype is a lack of ability to maintain the [Psi+] conformation. The N-terminus has a high glutamine/asparagine amount at 43%, while the average yeast protein only contains 9%. The N terminus is 114 amino acids long and is termed the prion forming domain (PrD). Over expression of the Sup35p gene can lead to [Psi+]. Both the N and M terminals and the C terminus form binding sites to Sup45p, giving a total of two. Also, in binding to Sup45p the [psi+] protein can cause it to aggregate and form a prion. Adenine Pathway The phenotypic differences between [psi-] and [psi+] is made clear when the ability of the cell to make adenine is tampered with. The buildup of P-ribosylamino imidazole (AIR) (a precursor in the adenine pathway in yeast) induces a red pigment in a yeast colony visible to the naked eye. In isogenic strains where the non-sense mutation is in the middle of either the gene ADE 2 or ADE 1 (enzymes involved in the pathway), the [psi-] strain has either build ups of P-ribosylamino imidazole (AIR), or P-ribosylamino imidazolecarboxylate (CAIR), respectively. Because CAIR converts back into AIR if the enzyme that catalyzes it to the next precursor is absent, either mutation will cause a red color in the [psi-] strain. The [psi+] strain appears white even when subjected to the same non-sense mutations. Thus, it is inferred that the eRF3 of the [psi+] is non-functional. This phenomenon is because the eRF3 in [psi-] is able to disconnect the ribosome effectively, so the enzyme cannot be properly synthesized. However, in the [psi+] strain, the enzyme is able to be synthesized enough so that the pathway still successfully produces adenine. See also Translation (genetics) Fungal Prions Prion Release factor Sup45p References