Haploid yeast cells MATa will produce and excrete only the factor "a" and will only react to factor "alpha" (and vice-versa for MATalpha). So if you are working with MATa cells you can only trigger a reaction with the factor alpha. If you change your mating type from MATa to MATalpha, there is no point of using the factor alpha.

If you really want to change the mating type, the simplest would be to generate diploids through crossing with a MATalpha (of the same background), make them sporulate and dissect the tetrads to check for your desired mating type.

One alternative: in wildtype yeast strains, there is a gene called HO that allow them to change mating type at each division. Most lab strains are mutated for this gene to maintain only one mating type. You could introduce this HO gene on a plasmid and transform it into your yeast to induce change of mating type. But be aware that before proceeding you will need (1) to lose the plasmid (in rich media) to avoid permanent switching of mating type and (2) make sure you isolate single colonies to work with haploid and not diploid cells (because once transformed with HO you will have a mix of MATa and MATaplha that can cross with each other).

Hope this is clear.

Jérémy Scutenaire Thank you so much for your insight! So my intention is to use chromosomal integration on the MatA type yeast to introduce the genes that encode the MatAlpha pre-pro secretion signal fused to genes for the production of a recombinant protein. My hope is that the the yeast's Endoplasmic reticulum will recognize the pre-pro secretion signal, cleave it off the recombinant protein, and secrete the recombinant protein- as is done with actual mating factor Alpha in MatAlpha yeast. So my question is moreso, will the MatA type yeast be able to perform all of this since it is mimicking a process that occurs naturally in MatAlpha cells and not MatA cells?

Ok I understand more your application. It seems a very practical way of producing/secreting a recombinant protein. My only concern is that alpha factor is very small (13 amino acids) so compare to any other protein that you would like to produce, the secretion efficiency might be different. But if this has been done before in the literature then it is fine.

Theoretically, the only difference between MATa and alpha is just expression of the active MAT gene, that will lead to production of the mating factor and the appropriate receptor to react to the opposite mating type factor. In your case, if you want to introduce and produce the alpha factor inside a MATa yeast it might be a problem. To be honest I have no idea what will be the consequence of this hybrid situation, but yes I would recommend that you change the mating type to work with MATalpha cells. Otherwise why don't you work with diploid cells that naturally express both mating type factor?