The methylotrophic yeasts Hansenula polymorpha, Pichia pastoris and Ca
ndida boidinii have been developed as production systems for recombina
nt proteins. The favourable and most advantageous characteristics of t
hese species have resulted in an increasing number of biotechnological
applications. As a consequence, these species - especially H. polymor
pha and P. pastoris - are rapidly becoming the systems of choice for h
eterologous gene expression in yeast, Recent advances in the developme
nt of these yeasts as hosts for the production of heterologous protein
s have provided a catalogue of new applications, methods and system co
mponents.