Characterization of cis elements that regulate the expression of glnA in Synechococcus sp. strain PCC 7942

Abstract

The upstream noncoding region of the Synechococcus sp. strain PCC 7942 (hereafter referred to as Synechococcus 7942) glnA gene was fused to the cat gene in order to study the expression of glnA both in Synechococcus 7942 and in Escherichia coli. The lack of cat expression in E. coli indicated that the glnA promoter was not recognized by E. coli RNA polymerase. The fused construct was integrated into the Synechococcus 7942 chromosome at a neutral site. Expression of the cat reporter gene was regulated under various nitrogen conditions in a way similar to that of the glnA gene. A deletion introduced at the binding site of the NtcA regulatory protein abolished derepression of the glnA promoter during growth in nitrate and under nitrogen starvation. Deletion of the sequence between the transcription and translation start sites of glnA prevented the repression observed during growth in ammonium. These results indicate that the glnA promoter is subject to complex regulation that involves sequences upstream and downstream from the transcription start site.

NtcA represses transcription of gifA and gifB, genes that encode inhibitors of glutamine synthetase type I from Synechocystis sp. PCC 6803

“…We and others have previously shown that the transcription factor NtcA activates transcription from several cyanobacterial glnA promoters in the absence of ammonium (Frias et al ., 1994; Luque et al ., 1994; Cohen‐Kupiec et al ., 1995; Reyes et al ., 1997). Data presented in this work demonstrate that NtcA represses transcription of gifA and gifB genes in the absence of ammonium.…”

Ammonium assimilation in cyanobacteria

“…In general, glnA genes are transcribed at basal levels from NtcA-independent promoters, in the presence of ammonium. NtcA-dependent glnA promoters are induced in cells that use nitrate as nitrogen source, but maximal level of expression is usually reached under nitrogen starvation (Tumer et al 1983;Elmorjani et al 1992;Cohen-Kupiec et al 1993;Wagner et al 1993;Frias et al 1994;Cohen-Kupiec et al 1995;Reyes et al 1997). How this gradation of levels of activation is accomplished is probably related to the mechanism that controls NtcA activity and is discussed below.…”

Cloning, sequencing, and regulation of the global nitrogen regulator gene ntcA in the unicellular diazotrophic cyanobacterium Cyanothece sp. strain BH68K

“…1). It has been demonstrated in PCC 7942 and PCC 7120 that NtcA binds to the promoter region of and activates genes involved in nitrogen control such as glnA, nir, and ntcA itself (3,9,12,13). Given its similarity to the NtcA proteins from PCC 7942 and PCC 7120, it is possible that the Cyanothece NtcA protein may bind similar target sequences.…”