Abstract: A method for producing of a protein of interest (POI) in a yeast host cell that is modified to comprise within one or more expression cassettes heterologous nucleic acid molecules encoding helper factors and a gene of interest (GOI) encoding the POI, wherein: a) a first helper factor comprises at least 90% sequence identity to SEQ ID NO:1; b) a second helper factor comprises at east 90% sequence identity to SEQ ID NO:3; and c) a third helper factor comprises at least 90% sequence identity to SEQ ID NO:5; which method comprises (i) culturing said host cell in a culture medium under conditions to co-express said heterologous nucleic acid molecules and to secrete said POI into the host cell culture; and (ii) recovering the POI from the host cell culture.