Molecular mechanism for the operation of nitrogen control in cyanobacteria.
In cyanobacteria, ammonium exerts a negative regulation of the expression of proteins involved in the assimilation of nitrogen sources alternative to ammonium. In Synechococcus, mRNA levels of genes encoding proteins for nitrate and ammonium assimilation were observed to be negatively regulated by ammonium, and ammonium-regulated transcription start points were identified for those genes. The NtcA protein is a positive regulator of genes subjected to nitrogen control by ammonium. Mutants lacking NtcA exhibited only basal mRNA levels of the regulated genes, even in the absence of ammonium, indicating that NtcA exerts its regulatory action by positively influencing mRNA levels of the nitrogen-regulated genes. NtcA was observed to bind directly to the promoters of nitrogen-regulated genes, and the palindromic DNA sequence GTAN8TAC was identified as a sequence signature for NtcA-target sites. The structure of the nitrogen-, NtcA-regulated promoters of Synechococcus was determined to be constituted by a -10, Pribnow-like box in the form TAN3T, and an NtcA-binding site that substituted for the canonical -35 box.
Instituto de Bioquímica Vegetal y Fotosíntesis, CSIC-Universidad de Sevilla, Facultad de Biología, Spain.
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D000595:Amino Acid Sequence; D001426:Bacterial Proteins; D001483:Base Sequence; D000458:Cyanobacteria / Q000235:genetics*; D004268:DNA-Binding Proteins; D015964:Gene Expression Regulation, Bacterial; D008969:Molecular Sequence Data; D009566:Nitrates / Q000378:metabolism; D009584:Nitrogen / Q000378:metabolism*; D011401:Promoter Regions, Genetic / Q000235:genetics*; D011485:Protein Binding; D000644:Quaternary Ammonium Compounds / Q000378:metabolism; D012333:RNA, Messenger / Q000032:analysis; D014157:Transcription Factors / Q000235:genetics* / Q000378:metabolism; D014158:Transcription, Genetic
D001426:Bacterial Proteins; D004268:DNA-Binding Proteins; D009566:Nitrates; D000644:Quaternary Ammonium Compounds; D012333:RNA, Messenger; D014157:Transcription Factors; C075617:ntcA protein, Synechococcus; D009584:Nitrogen