The present invention relates to a DNA sequence which encodes a protein of interest which contains regions having a high content of codons which are poorly suited to yeasts, characterized in that a sufficient number of codons which are poorly suited to yeasts is replaced with corresponding codons which are well-suited to yeasts in the said regions having a high content of codons which are poorly suited to yeasts. The present invention relates, more specifically, to DNA sequences which originate from dicotyledonous or monocotyledonous plants, in particular plants of the graminae family which are selected, in particular, from among wheat, barley, oats, rice, maize, sorghum and cane sugar. The present invention also relates to transformed yeasts which contain a DNA sequence according to the invention.