Expression and localization of four putative fatty aldehyde dehydrogenases in Yarrowia lipolytica

English: The dimorphic fungus Yarrowia lipolytica is an n-alkane assimilating yeast. During nalkane oxidation toxic fatty aldehydes are formed that are further oxidized by fatty aldehyde dehydrogenases (FALDH) to carboxylic acids that then enter the β-oxidation pathway. Very little research emphasis has been placed on FALDHs in yeasts and their precise role in n-alkane metabolism. This study aimed at contributing to the limited knowledge of yeast FALDHs and in particular the four putative Y. lipolytica FALDHs (YlFALDH1 - 4) that were recently identified in the fully sequenced genome of Y. lipolytica E150. The contribution made from this study to YlFALDHs was with reference to their promoter expression and subcellular localization. The promoter and terminator of each YlFALDH was initially used to construct reporter cassettes in conjunction with β-galactosidase (lacZ) by utilizing the Sticky-end PCR (SEP) and Enzyme-free cloning methods. These two methods proved to be unsuitable for the expression study. The promoter region of each YlFALDH was then cloned into the pINA781 expression vector containing lacZ to study the expression further. With the aid the pINA781 integrative vector and qualitative plate assays, with 5-bromo-4-chloro-3- indolyl-β-D-galactosidase (X-gal), it was observed that the promoters of YlFALDH1 and 2 were inducible by dodecane and hexadecane but not by oleic acid, glucose or glycerol. The promoter of YlFALDH2 also seemed to display the same level of transcriptional strength as the inducible POX2 promoter. Induction of the YlFALDH3 and 4 promoters was not observed. Localization of the YlFALDH proteins was studied with the aid of green fluorescent protein (GFP) from Aequorea victoria and putative localization sequences (LS) from each YlFALDH isozyme. The putative Y. lipolytica LSs comprised of the last 150 bp of the COOH-terminal of the YlFALDH proteins. These LSs were modeled from Rattus norvegicus FALDH that possesses a 35 amino acid hydrophobic protein anchor at its COOH-terminal. For localization studies, chimerical JMP5 molecules were created with an inducible ICL1 promoter, GFP and putative Y. lipolytica LS from each isozyme. Chimerical molecules were also constructed with a pKOV136 vector that contained a constitutive TEF promoter, a GFP-LS fragment (from a JMP5-chimera) and LIP2 terminator. No fluorescence was observed with epifluorescence or confocal laser microscopy when either of the JMP5- or pKOV136-chimeras were transformed into Y. lipolytica E150 and Po1g respectively. Consequently the subcellular localization could not be identified.