Journal of Clinical and Cellular Immunology
Open Access
ISSN: 2155-9899
ISSN: 2155-9899
Ankita Srivastava and Sudha Bhattacharya
Accepted Abstracts: J Clin Cell Immunol
Initiation of rDNA transcription requires the assembly of a specific multi-protein complex at rDNA promoter containing the RNA Polymerase-I (Pol-I) with many auxiliary factors. RNA Pol-I forms transcriptionally active enzyme, in association with a factor known as Rrn3P in yeast and Transcription Initiation Factor IA (TIFIA, Rrn3P homologue) in mammals. TIF-IA interacts with RPA43, a unique subunit of Pol I, and with two Pol I-specific TAF (TATA binding protein-associated factors), thereby serving as a bridge between Pol I and the pre-initiation complex at the rDNA promoter. TIFIA is phosphorylated at multiple sites, and signals in response to that affect cell proliferation and metabolism. In E. histolytica , the rRNA genes are present exclusively on 24.5 kb circular extra chromosomal plasmid named as EhR1. EhR1 contains two rDNA repeats (I & II), which are arranged palindromically, and separated by upstream and downstream spacers. The protein factors involved in regulation of rDNA transcription in E. histolytica are not known. We have identified and characterized the E. histolytica equivalent of the transcription initiation factor TIF-1A (EhTIFIA) which is known in other systems to control the initiation of rDNA transcription. EhTIFIA was identified by sequence analysis and have cloned and expressed the gene in E. coli. Immuno- localization studies showed, EhTIFIA co-localizes partially with Ehfibrillarin and the RNA Pol I specific subunit (EhRPA12) both of them are in the nucleolus (in eukaryotic cells), which in E. histolytica is located at the nuclear periphery. EhTIFIA was extensively phosphorylated in presence of E. histolytica nuclear extract and one phosphorylation site at S461 was identified through mass spectroscopy. EhTIFIA was shown to interact with EhRPA12 both in vivo and in vitro. Mass spectroscopy data showed the major interacting partners of EhTIFIA to be RNA Pol-I specific subunits as well as some nucleolar proteins Further, we are trying to characterize EhTIFIA in relation to RNA Polymerase-I transcription regulation. Our study demonstrates presence of similar transcriptional machinery in primitive E. histolytica as in higher eukaryotes with certain structural and functional reform.