Title Differential Expression of citA Gene Encoding the Mitochondrial Citrate Synthase of Aspergillus nidulans in Response to Developmental Status and Carbon Sources
Author In Sook Min1, Ji Young Bang1, Soon Won Seo1, Cheong Ho Lee2, and Pil Jae Maeng1*
Address 1Department of Microbiology & Molecular Biology, Chungnam National University, Daejeon 305-764, Republic of Korea, 2KT&G Central Research Institute, Daejeon 305-345, Republic of Korea
Bibliography Journal of Microbiology, 48(2),188-198, 2010,
Key Words A. nidulans, citrate synthase, citA, differential expression, carbon catabolite repression, mitochondrial targeting
Abstract As an extension of our previous studies on the mitochondrial citrate synthase of Aspergillus nidulans and cloning of its coding gene (citA), we analyzed differential expression of citA in response to the progress of development and change of carbon source. The cDNA consisted of 1,700 nucleotides and was predicted to encode a 474-amino acid protein. By comparing the cDNA sequence with the corresponding genomic sequence, we confirmed that citA gene contains 7 introns and that its transcription starts at position -26 (26-nucleotide upstream from the initiation codon). Four putative CreA binding motifs and three putative stress-response elements (STREs) were found within the 1.45-kb citA promoter region. The mode of citA expression was examined by both Northern blot and confocal microscopy using green fluorescent protein (sGFP) as a vital reporter. During vegetative growth and asexual development, the expression of citA was ubiqiutous throughout the whole fungal body including mycelia and conidiophores. During sexual development, the expression of citA was quite strong in cleistothecial shells, but significantly weak in the content of cleistothecia including ascospores. Acetate showed a strong inductive effect on citA expression, which is subjected to carbon catabolite repression (CCR) caused by glucose. The recombinant fusion protein CitA40::sGFP (sGFP containing the 40-amino acid N-terminal segment of CitA) was localized into mitochondria, which supports that a mitochondrial targeting signal is included within the 40-amino acid N-terminal segment of CitA.