Hansenula polymorpha mutants and process for the preparation of recombinant proteins using the same

Disclosed are Hansenula polymorpha mutants useful as host cells through which various proteins can be produced as being intact at high yield and a process for preparing recombinant proteins using the host cells. Using various vectors, Hansenula polymorpha is made to be a mutant which is deprived of methanol assimilating ability and incapable of utilizing methanol as a carbon source. This Hansenula polymorpha mutant is used as a high yield host to produce recombinant proteins without continuous feeding of methanol, with the aid of an expression cassette carrying a promoter capable of inducing the expression at a low concentration of methanol. Further, the mutant is also lacking in carboxypeptidase Y, protease Y and/or carboxypeptidase a activity, so the recombinant protein of interest is not degraded at its carboxyl terminal when being expressed in the cell. Thus, intact recombinant protein can be obtained. Also, there is disclosed a pop-out technique in which a recombinant protein expression cassette is inserted into a MOX gene site of the mutant and is allowed to pop out therefrom, thereby utilizing the mutant as a host for general use in producing various proteins of interest.