Photosynthetic electron transport controls nitrogen assimilation in cyanobacteria by means of posttranslational modification of the glnB gene product.

Abstract

A glnB gene is identified in the cyanobacterium Synechococcus sp. PCC 7942, and its gene product is found to be covalently modified as a result of imbalance in electron transfer in photosynthesis, where photosystem II is favored over photosystem I. The gene was cloned and sequenced and found to encode a polypeptide of 112 amino acid residues, whose sequence shows a high degree of similarity to the Escherichia coli regulatory protein, PI,. In E. coli, PI, is involved in signal transduction in transcriptional and posttranslational regulation of nitrogen assimilation. Increase in ammonium ion concentration is shown to decrease covalent modification of the Synechococcus PI, protein, as in enteric bacteria. We therefore propose that the photosynthetic electron transport chain may regulate the pathway of nitrogen assimilation in cyanobacteria by means of posttranslational, covalent modification of the glnB gene product. The existence of the glnB gene in different strains of cyanobacteria is demonstrated and its implications are discussed.

An alternative PII protein in the regulation of glutamine synthetase in Escherichia coli

“…X84158); Hi, Haemophilus influenzae (Fleischmann et al, 1995); Ss, Synechococcus sp. PCC 7942 (Tsinoremas et al, 1991); Bs, B. subtilis (Wray, et al, 1994); Ma, Methanobacterium thermoautotrophicus (GenBank Accession no. X87971); Ml, Methanococcus thermolithotrophicus (Souillard and Sibold, 1989); Mb1 and Mb2, first and second nifH region of Methanosarcina barkeri 227 (Sibold et al, 1991); Mi, Methanobacterium ivanovii (Sibold et al, 1991).…”

Tansley Review No. 107. Heterocyst and akinete differentiation in cyanobacteria

“…In enteric bacteria, the synthesis and activity of GS is controlled by the two-component Ntr (nitrogen regulation) system in which the glnB gene product, the P II protein, transmits the N status of the cell to the Ntr proteins (Merrick & Edwards, 1995). P II -like proteins have been characterized from both unicellular and filamentous cyanobacteria (Tsinoremas et al, 1991 ;Liotenberg et al, 1996 ;Garcı! a-Domı!…”

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

“…The P II protein has been found in cyanobacteria, and its presence suggests the existence of a cyanobacterial Ntr system (21). However, repeated efforts to isolate ntrB and ntrC homologs in cyanobacteria have failed, and the precise role of P II in signal transduction in cyanobacteria is unknown (20).…”