Growth Phase-dependent Activation of Nitrogen-related Genes by a Control Network of Group 1 and Group 2 σ Factors in a Cyanobacterium

Sousuke Imamura,Kan Tanaka,Makoto Shirai,Munehiko Asayama

doi:10.1074/jbc.m509639200

Sousuke Imamura, Kan Tanaka + Show 2 more

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https://doi.org/10.1074/jbc.m509639200

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Abstract

It has been reported that an RNA polymerase sigma factor, SigC, mainly contributes to specific transcription from the promoter PglnB-54,-53 under nitrogen-deprived conditions during the stationary phase of cell growth in the cyanobacterium Synechocystis sp. strain PCC 6803 (Asayama, M., Imamura, S., Yoshihara, S., Miyazaki, A., Yoshida, N., Sazuka, T., Kaneko, T., Ohara, O., Tabata, S., Osanai, T., Tanaka, K., Takahashi, H., and Shirai, M. (2004) Biosci. Biotechnol. Biochem. 68, 477-487). In this study, we further examined the functions of group 2 sigma factors of RNA polymerase in NtcA-dependent nitrogen-related gene expression in PCC 6803. Results indicated that SigB and SigC contribute to the transcription from PglnB-54,-53 with a sigma factor replaced in a growth phase-dependent manner. We also confirmed the contribution of SigB and SigC to the transcription of other NtcA-dependent genes, glnA, sigE, and amt1, as in the case of glnB. On the other hand, the transcription of glnN was dependent on SigB and SigE. In the SigB and SigC-based regulation, the level of SigB increased, but that of SigC was constant under conditions of nitrogen deprivation. Furthermore, it was found that SigC negatively and positively regulates the level of SigB in the log and stationary phase, respectively. SigC also had a positive effect on the level of sigB transcript during the stationary phase. In contrast, SigB acts positively on SigC levels in both growth phases. These results and previous findings indicated that multiple group 2 sigma factors take part in the control of NtcA-dependent nitrogen-related gene expression in cooperation with a group 1 sigma factor, SigA.

Highlights

The RNA polymerase holoenzyme of eubacteria consists of a core enzyme and ␴ factor [1]
The regulation of nitrogen assimilation could differ between enteric bacteria and cyanobacteria, because no homologues of RpoN-type ␴ factor, NtrB/NtrC, and glutamine synthetase adenylyltransferase have been identified in cyanobacteria
Growth Phase-dependent Regulation of the glnB Transcript by SigB and SigC—Our previous study has indicated that SigC controls synthesis of the glnB transcript from PglnB-54,53 induced by nitrogen deprivation in the stationary phase

Summary

The abbreviations used are

2-OG, 2-oxoglutarate; RNAP, RNA polymerase; QRT-PCR, quantitative real time PCR; IS, integration site; ppGpp, guanosine 3,5-(bis)pyrophosphate; ⌬B, ⌬C, ⌬D, and ⌬E, sigB, sigC, sigD, and sigE knock-out strain, respectively; Log, midexponential phase; Sta, stationary phase; ϪN and ϩN, without and with nitrogen, respectively; GS, glutamine synthase; GOGAT, glutamate synthase. Our recent study revealed that transcription from the glnB (encoding PII) [16] promoter (PglnB-54,-53) is due to specific recognition by a PCC 6803 group 2 ␴ factor, SigC, in the stationary (postexponential) growth phase under nitrogen-deprived conditions [17]. We characterized the specificity with which PCC 6803 group 2 ␴ factors recognize other NtcA-dependent promoters, glnA, sigE, amt, and glnN We summarize these results and present a possible regulatory network of group 1 and group 2 ␴ factors for the transcription of NtcA-dependent nitrogen-related genes

EXPERIMENTAL PROCEDURES

RESULTS

DISCUSSION