tailieunhanh - Báo cáo khoa học: Experimental and steady-state analysis of the GAL regulatory system in Kluyveromyces lactis

The galactose uptake mechanism in yeast is a well-studied regulatory net-work. The regulatory players in the galactose regulatory mechanism (GAL system) are conserved in Saccharomyces cerevisiae and Kluyveromyces lactis, but the molecular mechanisms that occur as a result of the molecular interactions between them are different. | ỊFEBS Journal Experimental and steady-state analysis of the GAL regulatory system in Kluyveromyces lactis Venkat R. Pannala Sharad Bhartiya and Kareenhalli V. Venkatesh Department of ChemicalEngineering Indian Institute of Technology Bombay Mumbai India Keywords galactose GAL system Kluyveromyces lactis Saccharomyces cerevisiae steadystate model Correspondence S. Bhartiya K. V. Venkatesh Department of ChemicalEngineering Indian Institute of Technology Bombay Powai Mumbai-400076 India Fax 91 22 25726895 Tel 91 22 25767225 E-mail venks@ Received 10 December 2009 revised 7 May 2010 accepted 12 May 2010 doi The galactose uptake mechanism in yeast is a well-studied regulatory network. The regulatory players in the galactose regulatory mechanism GAL system are conserved in Saccharomyces cerevisiae and Kluyveromyces lactis but the molecular mechanisms that occur as a result of the molecular interactions between them are different. The key differences in the GAL system of K. lactis relative to that of S. cerevisiae are a the autoregulation of KIGAL4 b the dual role of KlGal1p as a metabolizing enzyme as well as a galactose-sensing protein c the shuttling of KlGal1p between nucleus and cytoplasm and d the nuclear confinement of KlGal80p. A steady-state model was used to elucidate the roles of these molecular mechanisms in the transcriptional response of the GAL system. The steadystate results were validated experimentally using measurements of b-galac-tosidase to represent the expression for genes having two binding sites. The results showed that the autoregulation of the synthesis of activator KlGal4p is responsible for the leaky expression of GAL genes even at high glucose concentrations. Furthermore GAL gene expression in K. lactis shows low expression levels because of the limiting function of the bifunctional protein KlGal1p towards the induction process in order to cope with the need for the metabolism of lactose .