Abstract: The present invention relates to a sulfolobus expression vector comprising: (a) sulfolobus origin of replication; (b) the genes encoding the structural proteins and the site-specific integrase of SSV1, SSV2 or pSSVx, operatively linked to expression control sequences and a packaging signal; (c) one or more selectable marker gene(s), operatively linked to sulfolobus expression control sequences; and (d) a sulfolobus promoter followed 3? by a restriction enzyme recognition site or a multiple cloning site for insertion of a gene of interest and optionally a 3? regulatory element. Moreover, the present invention relates to a shuttle vector comprising the sequences of the expression vector of the invention and additional sequences for propagation and selection in E. coli, wherein the additional sequences comprise (a) an E. coli on of replication; and (b) a marker for selection in E. coli.