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: ( * See Patent for Tabular Presentation * ) PS H gene being the gene coding for hirudin or one of its variants, Str is a DNA sequence containing the signals which provide for the transcription of the H gene by yeast, Lex is a leader sequence needed in order to obtain the excretion of the gene product, Scl 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.