The present invention relates to a efficient expression of a protein, particularly, hirudin; a protein precursor comprising a signal sequence and the sequence of aa.sub.X-hirudin, wherein aa.sub.X is a selected amino acid, and aa.sub.X is preferably leucine; to its preparation and use; and to processes for finding signal sequences for secretory expression of any desired protein in E coli; and to processes for the secretory expression of any desired protein in E coli.