Basal transcription factors in Giardia lamblia

TROCHINE ANDREA; ZELUS, DOMINIQUE; CRIBB PAMELA; LUJAN HUGO; SERRA ESTEBAN

Caxambu. MG. Brasil

Congreso; XXIX Annual Meeting on Basic Research in Chagas Disease- XVIII Meeting of the Brazilian Society of Protozoology.; 2002

Brazilian Society of Protozoology.

Giardia lamblia is a highly prevalent human protozoan pathogen and one of the earliest diverging eukaryotic cells. It has a small and compact genome. Only one intron sequence has been reported in Giardia genes; intergenic regions are negligible (often <25 bp), and the untranslated regions of mRNAs analyzed so far are typically short. Very little is known about the mechanism and regulation of transcription initiation in Giardia. Neither regulatory transcription factors nor strong promoter consensus sequences have been reported up to now. This makes us hypothesize that the control of gene expression could be regulated at the level of the transcription initiation complex. To explore this hypothesis we performed a BLAST search for components of the basal complex in G. lamblia genome database. We identified several sequences related with eukaryotic and archaeal basal factors including TBP, TFIIB, TFIIH, TAFII100, among others; though with low sequence identity (less than 30%). The coding regions of putative TBP and TFIIB factors were amplified by PCR and cloned in pGEX expression vectors. For further biochemical studies the fusion proteins were purified and the GST tag were released with thrombin. Southern blotting experiments showed that both genes are present as single copies in G. lamblia genome. Our results lead us to the proposal that Giardia may possess a simplified version of the basal transcription machinery present in eukaryotes, resembling the initiation complex found in archaea.