Fuente: WIPO "biotechnology" The use of a means to vary Ubc4p or Ubc5p activity in a fungal cell to control the copy number of a plasmid in the cell. The level of Ubc4p or Ubc5p activity may be reduced/abolished (for example by gene deletion, mutagenesis to provide a less active protein, production of antisense mRNA or production of competitive peptides) to raise the copy number and increase yield of a protein encoded by the plasmid.