The invention relates to nucleic acids encoding polypeptides having amylase activity, and methods for making and using them. In one aspect, the polypeptides having amylase activity have increased activity and stability at acidic, neutral and alkaline pH and increased temperature. In one aspect, the invention provides methods for producing an alcohol, for producing a high-maltose or a high-glucose syrup or a mixed syrup, for liquifying a starch-comprising composition, comprising use of polypeptides encoded by the nucleic acids of this invention.