Axl1p gene product (Saccharomyces cerevisiae)

This chapter describes the structural chemistry and the biological aspects of Axllp gene product (Saccharomyces cerevisiae). The yeast Saccharomyces cerevisiae generates progeny by the process of budding. The AXLl gene was initially identified in a genetic screen as being required for the maintenance of the axial (AXL) budding pattern that is characteristic of haploid yeast. In the absence of the AXLl gene product (Axllp), haploid yeast undergo a bipolar budding pattern that is typical of diploid yeast. In addition to having a role in axial budding, Axllp is required for the production of the a-factor mating pheromone by MATa haploid cells. Genetic and metabolic labeling studies support a proteolytic role for Axllp in the production of the a-factor mating pheromone. The bioactive mature pheromone is a famesylated and carboxylmethylated dodecapeptide that derives from a precursor after extensive post-translational modification. At the C-terminus of the precursor, a canonical CaaX motif is present that directs an ordered series of post-translational modifications. The basis for the classification of Axllp as a protease relies mostly on genetic and metabolic labeling studies.