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The discovery of arrestin-mediated biased signalling mechanisms for mammalian G-protein coupled receptors (GPCRs) has revolutionized the field over the last decade. Now, with the recent demonstration of a role for a-arrestins in internalization of the yeast pheromone GPCR, Ste2p, the possibility of arrestin-mediated alternate GPCR functionalities in yeast also follows. Here, the effects of knockout and complementation of yeast a-arrestin expression during mating are reported. Although minor effects on classical pheromone-related signalling are noted for a few arrestins, much stronger effects were observed downstream of cell cycle arrest, in particular linking Ldb19 (Art1) to mediation of zygote formation. Subsequent phenotypic observations linked this activity to more pronounced projection formation in an Art1 complemented noncuple a-arrestin knockout line, compared to the knockout-line alone, or either of the Art3 or Art6 complemented lines. Together with the observation of ligand-stimulated localization of Art-GFP to the mating projection, a possible role for this arrestin-like protein in projection formation is supported. While leaving the full mechanism of alternate Art1 functionality to be elucidated, together these findings implicate Art1 in selective regulation of mating events downstream of receptor internalization and cell cycle arrest, leading to schmoo, and ultimately zygote formation. [ABSTRACT FROM AUTHOR]