The invention generally relates to novel and improved nucleic acid sequences encoding a polypeptide or protein having the enzymatic activity of a phytase and methods for effectively expressing such enzymes in a host cell.In a first aspect, the present invention relates an isolated nucleic acid molecule i) comprising the nucleotide sequence according to SEQ ID NO: 1 encoding a protein with phytase activity or ii) having a sequence identity of at least 78 % to a nucleotide sequence according to SEQ ID NO: 1 encoding a protein with phytase activity.The present invention also relates to an expression construct or a vector comprising the above mentioned isolated nucleic acid molecule. The present invention further relates to a method of producing a protein having the enzymatic activity of a phytase comprising the steps of:a) introducing into a host cell a vector comprising:i) elements regulating the expression that are functional in the host cell； andii) operatively linked thereto a nucleic acid molecule according to the invention；b) cultivating the host cells obtained in step a) under conditions suitable for expression of the protein, and optionallyc) recovering the protein produced in step b) from the cell culture.The present invention further relates to proteins obtained by the method according to the invention and the use thereof for the manufacture of additives for animal feed.
