Bioinfo Publications 197 NUCLEOSIDE DIPHOSPHATE KINASE GENE IS EXPRESSED THROUGH MULTIPLE TRAN- SCRIPTS IN Mycobacterium smegmatis International Journal of Microbiology Research ISSN: 0975-5276 & E-ISSN:0975-9174, Volume 4, Issue 4, 2012, pp.-197-206. Available online at http://www.bioinfo.in/contents.php?id=27 MUTHU ARUMUGAM, DEEPAK ANAND, NAMPERUMALSAMY VIJAYARANGAN, CHANDRASEKARAN ANBUKAYALVIZHI, MEGHA RAO, SRINIVASAN VIJAY, HARYADI RAJESWARI AND PARTHASARATHI AJIT KUMAR Department of Microbiology and Cell Biology, Indian Institute of Science, Bangalore-560012, Karnataka, India. *Corresponding Author: Email- ajit@mcbl.iisc.ernet.in Received: March 15, 2012; Accepted: May 03, 2012 Abstract- Nucleoside diphosphate kinase, NDK, plays a vital role in maintaining pools of nucleoside triphosphates and their respective de- oxynucleoside triphosphates for the synthesis of RNA and DNA. Transcriptional regulation of ndk in mycoacteria remains unknown, although modulation of ndk expression under stress conditions involving DNA and, RNA synthesis arrest and cell division arrest had been studied in several bacterial systems. Therefore, in the present study, the start sites of transcription of ndk of Mycobacterium smegmatis (Msmndk) were identified and putative promoter regions were predicted. Using transcriptional fusions of the cloned putative promoter regions to myco- bacterial codon-optimised reporter gene, gfpm 2+ , promoter activity was examined under active phase of growth, nutrient starvation and other stress conditions involving DNA replication inhibition and cell division arrest. Msmndk was found to be expressed through two transcripts, T1 and T2, arising from P1 and P2 promoters, respectively. Both the promoters belonged to C group of mycobacterial promoters, which do not possess consensus to any known canonical sigma factor recognition sequences. The levels of T2, but not of T1, were found to be low under the different stress conditions studied. The data documents modulation of ndk transcripts in mycobacteria. Key words- Nucleoside diphosphate kinase transcripts, Mycobacterium smegmatis, Transcription start site, Primer extension, Hydroxyurea, Phenethyl alcohol, nutrient-depleted stationary phase. International Journal of Microbiology Research ISSN: 0975-5276 & E-ISSN:0975-9174, Volume 4, Issue 4, 2012 Introduction Nucleoside diphosphate kinase (NDK), originally discovered by Krebs and Hems[1] and Berg and Joklik [2], catalyses the transfer of a 5’ terminal phosphate from ATP or GTP to a nucleoside di- phosphate (NDP), via a phosphohistidine enzyme intermediate [3]. The primary role of NDK is to maintain nucleoside triphos- phates (NTPs) and their deoxy derivatives (dNTPs) pool for the synthesis of RNA and DNA and for other biosynthetic processes in bacteria to humans [4-6]. Besides this fundamental role in nu- cleotide metabolism, NDK has been implicated in many other cellular functions. The ndk transcription gets downregulated by the phosphorylated ArcA under redox conditions in Escherichia coli [7], in the classical biotype O1 of Vibrio cholerae but not in O1 El Tor biotype [8], and in the bacterial pathogen, Chlamydia tra- chomatis, during the developmental cycle [9]. Similarly, E. coli ndk (Econdk) is repressed by the DNA-bending protein, HU, under aerobic conditions [10], by the global regulator, FNR, under an- aerobic conditions [11], and by cyclic AMP receptor protein (CRP) in vitro [12]. Repression of Salmonella enterica serovar Typhimuri- um ndk by the DNA-binding and transcription regulatory protein, Fis [13] lowers GTP levels, thereby regulating pppGpp and ppGpp pool size. On the contrary, in Pseudomonas aeruginosa, AlgQ, which modulates the levels of alginate [14], upregulates ndk, thereby positively regulates the levels of GTP, ppGpp, and inor- ganic polyphosphate (polyp) [15, 16]. Similarly, under osmotic and oxidative stress conditions, ndk is upregulated in order to restore cell homeostasis in Sinorhizobium meliloti, carrying a mutation in the outer membrane protein, TolC [17]. Citation: Muthu Arumugam, et al. (2012) Nucleoside diphosphate kinase gene is expressed through multiple transcripts in Mycobacterium smegmatis. International Journal of Microbiology Research, ISSN: 0975-5276 & E-ISSN:0975-9174, Volume 4, Issue 4, pp.-197-206. Copyright: Copyright©2012 Muthu Arumugam, et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.