A schematic representation of common aspects of the procedure that Tanaka et al.  and King and Diaz-Avalos  used to generate multiple [PSI+] strains by converting Sup35p protein to different aggregating conformations in vitro. The [psi-] budding yeast cells (left) containing normal Sup35p (circles) were made into spheroplasts (lacking some of the cell wall; middle) into which preformed conformations of a recombinant amino-terminal fragment of Sup35p (squares and triangles) were introduced. This leads to a [PSI+] state (right), as assessed by plating on a rich medium containing trace amounts of adenine; [PSI+] cells produce white colonies on this medium whereas [psi-] cells produce red colonies (not shown). Different conformations of Sup35p gave rise to phenotypically distinct strains of [PSI+] cells.