The isoprenoid pathway in yeasts is important not only for sterol biosynthesis but also for the production of non-sterol molecules, deriving from farnesyl diphosphate (FPP), implicated in N-glycosylation and biosynthesis of heme and ubiquinones. FPP formed from mevalonate in a reaction catalyzed by FPP synthase (Erg20p). In order to investigate the regulation of Erg20p in Saccharomyces cerevisiae, a two-hybrid screen was used for its searching and five interacting proteins were identified. Subsequently it was showed that Yta7p is a membrane-associated protein localized both to the nucleus and to the endoplasmic reticulum. Deletion of Yta7 affected the enzymatic activity of cis- prenyltransferase (the enzyme that utilizes FPP for dolichol biosynthesis) and the cellular levels of isoprenoid compounds. Additionally, it rendered cells hypersensitive to lovastatin, an inhibitor of 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMGR) that acts upstream of FPP synthase in the isoprenoid pathway. While HMGR is encoded by two genes, HMG1 and HMG2, only HMG2 overexpression was able to restore growth of the yta7- cells in the presence of lovastatin. Moreover, the expression level of the S. cerevisiae YTA7 gene was altered upon impairment of the isoprenoid pathway not only by lovastatin but also by zaragozic acid, an inhibitor of squalene synthase (Kuranda et al., 2009).

All enzymes involved in carotenoid biosynthesis are membrane-associated or integrated into membranes. Moreover, carotenoid biosynthesis requires the interaction of multiple gene products. At present more than 150 genes, encoding 24 different crt enzymes involved in carotenogenic branch of isoprenoid pathway, have been isolated from bacteria, plants, algae and fungi. The availability of a large number of carotenogenic genes makes it possible to modify and engineer the carotenoid biosynthetic pathways in microorganisms. A number of genetically modified microbes, e. g. Candida utilis, Escherichia coli, Saccharomyces cerevisiae, Zymomonas mobilis, etc. have been studied for carotenoid production (Wang et al. 2000; Schmidt-Dannert, 2000; Lee & Schmidt-Dannert, 2002; Sandmann 2001). However, lack of sufficient precursors (such as IDP, DMADP and GGDP) and limited carotenoid storage capability is the main task how to exploate these organisms as commercial carotenoid producers. Therefore, effort has been focuced on increasing the isoprenoid central flux and levels of carotenoid precursors. For example, overexpression of the IDP isomerase (idi — catalyzes the isomerization of IDP to DMAP) together with an archaebacterial multifunctional GGDP synthase (gps — converts IDP and DMADP directly to GGDP) resulted in a 50-fold increase of astaxanthin production in E. coli (Wang et al., 2000).

By combination of genes from different organisms with different carotenoid biosynthetic branches, novel carotenoids not found in any other pathway can be synthesized. Most Mucor species accumulate |3-carotene as the main carotenoid. The crtW and crtZ astaxanthin biosynthesis genes from Agrobacterium aurantiacum were placed under the control of Mucor circinelloides expression signals. Transformants that exhibited altered carotene production were isolated and analyzed. Studies revealed the presence of new carotenoid compounds and intermediates among the transformants (Papp et al., 2006). Fusarium sporotrichioides was genetically modified for lycopen production by redirecting of the isoprenoid pathway toward the synthesis of carotenoids and introducing genes from the bacterium Erwinia uredovora (Leathers et al, 2004). Carotenoid biosynthetic pathway of astaxanthin producers of Phaffia/Xanthophyllomyces strains has also been engineered and several genes, such as phytoene desaturase, isopentenyl diphosphate isomerase and epoxide hydrolase were isolated and expressed in E. coli (Verdoes et al., 2003; Lukacz, 2006).