Study On Function Of PipX In Anabaena PCC 7120

Cyanobacteria are a diverse group of eubacterial that are characterized by the ability to perform oxygen-evolving photosynthesis.Synechococcus sp.PCC 7942 is a unicellular cyanobacterium that don’t perform nitrogen fixation.Anabaena sp.PCC 7120,a filamentous cyanobacterium,can perform nitrogen fixation in differentiated cells called heterocysts.Although the morphology and the ability to develop into N2-fixing heterocysts vary greatly among cyanobacteria,they share many common metabolic characteristics.PipⅩ,a protein that interacts with PⅡand NtcA in a 2-oxoglutarate dependent manner in Synechococcus sp.PCC 7942,and plays a role in the nitrogen metabolism via the transcription regulation by NtcA in Synechococcus PCC 7942.In addition,PipⅩhas a positive effect on the transcriptional activity of two NtcA-dependent peomoters,those of glnB and glnN..This study focused on the study of the function of PipⅩand its effect on NtcA transcriptional activity in Anabaena sp.PCC 7120.PipⅩis an unstable,alkaline and hydrophilic 92 a.a.protein.The major secondary structure was composed of three Alpha helixs with no identified structure domain.The results of Real Time PCR showed different expression profiles o fpipⅩin the wide type and hetR mutants in different nitrogen conditions.After combined nitrogen deprivation, the expression ofpipXwas extraordinarily enhanced in wide type,and arrived at a high expressional level 12 h after combined nitrogen step-down which was 20 times that of 0 h. Whilethere was only minor upregulation ofpipX expression in hetR mutant.All the results above suggested that pipⅩwas involved in heterocyst differentiation,and the up-regulation of pipⅩwas influenced by hetR in a direct or an indirect way after combined nitrogen deprivation.This study also utilized EMSA to analyze the effect of PipⅩon ntcA transcriptional activity in vitro.According to the results,we found that PipⅩcould activate the transcriptional regulation of NtcA.On one hand PipⅩstimulated the binding of NtcA to the non-canonical DNA sequences,on the other hand PipⅩenhanced the DNA-binding activity of NtcA,especially for the more conserved non-canonical DNA sequences.