Significant progress has been made in the development of powerful sequence analysis tools. Although often optimized for sequences from more traditional model organisms, they offer great value for comparative studies that include evolutionarily divergent sequences. They should be used cautiously, however, with awareness of their limitations, which are largely a reflection of current scientific knowledge and understanding of genome structure. As the diversity of available sequence data continues to increase, it will drive refinements and development of new tools and provide important insights into the evolution and essential mechanisms of gene expression regulation.  Regulated multicistronic expression technology for mammalian metabolic engineering Contemporary basic research is rapidly revealing increasingly complex molecular regulatory networks which are often interconnected via key signal integrators. These connections among regulatory and catalytic networks often frustrate bioengineers as promising metabolic engineering strategies are bypassed by compensatory metabolic responses or cause unexpected, undesired outcomes such as apoptosis, product protein degradation or inappropriate post- translational modification. Therefore, for metabolic engineering to achieve greater success in mammalian cell culture processes and to become important for future applications such as gene therapy and tissue engineering, this technology must be enhanced to allow simultaneous, in cases conditional, reshaping of metabolic pathways to access difficult-to-attain cell states. Recent advances in this new territory of multigene metabolic engineering are intimately linked to the development of multicistronic expression technology which allows the simultaneous, and in some cases, regulated expression of several genes in mammalian cells. Here we review recent achievements in multicistronic expression technology in view of multigene metabolic engineering. There are two general levels of genetic engineering in which a suitable production cell line is generated; (i) stable introduction of the genetic information for the product protein and (ii) an optional metabolic engineering step to improve cellular activities by the manipulation of enzymatic, transport, and regulatory functions of the cell (Bailey, 1991) . Metabolic engineering of animal cells has already been proven useful for improving diverse key characteristics of cultured cells including cell viability (apoptosis engineering: Cotter and Al-Rubeai, 1995; Mastrangelo and Betenbaugh, 1998) , product quality (glycosylation engineering: Bailey et al., 1998; Jenkins et al., 1996) , product yield (controlled proliferation technology: Fussenegger et al., 1997a; Fussenegger et al., 1998a; Fussenegger et al., 1998b; Papoutsakis, 1998) and growth in protein-free medium (cell-cycle engi- * Author for all correspondence.