Abstract: The invention relates to a functional DNA block by means of which hirudin may be prepared from yeast, which block contains at least the sequence:-S.sub.tr -L.sub.ex -S.sub.cl -H geneH gene being the gene coding for hirudin or one of its variants,S.sub.tr is a DNA sequence containing the signals which provide for the transcription of the H gene by yeast,L.sub.ex is a leader sequence needed in order to obtain the excretion of the gene product,S.sub.cl is a DNA sequence coding for the site of cleavage by yscF proteinase, which cleavage site is unique and situated in the hirudin precursor immediately upstream from the H gene.The invention relates more especially to a functional DNA block in which the H gene codes for HV1.