Pseudomonas saccharophila G4-forming amylase (PS4), and variants thereof, advantageously can be used in an enzyme-catalyzed high temperature liquefaction step to produce ethanol from starch, e.g., cornstarch. PS4 produces significant amounts of maltotrioses, which can be utilized by S. cerevisiae in a subsequent fermentation step to produce ethanol. This property of PS4 advantageously allows ethanol to be produced from liquefacted starch in the absence of a saccharification step. PS4 variants are provided that exhibit improved properties, such as thermostability and/or altered exo-specific and endo-specific amylase activity.
