Role of a Ubiquitin-Like Modification in Polarized Morphogenesis

Abstract

Type I ubiquitin-like proteins constitute a family of protein modifiers. Here we report the identification of a posttranslational protein modifier from Saccharomyces cerevisiae , Hub1. Overexpression of Hub1 resulted in enhanced conjugate formation when its carboxyl-terminal residue was deleted, suggesting that mature Hub1 may be produced by proteolytic processing. In vivo targets of Hub1 conjugation included cell polarity factors Sph1 and Hbt1. In the hub1 Δ mutant, the subcellular localization of both Hbt1 and Sph1 was disrupted, and cell polarization during the formation of mating projections was defective. Consistent with these polarization defects, the hub1 Δ mutant was deficient in mating.