A gene coding for a putative sigma 54 activator is developmentally regulated in Caulobacter crescentus

Abstract

In Caulobacter crescentus, the alternative sigma factor 54 plays an important role in the expression of late flagellar genes.54 -dependent genes are temporally and spatially controlled, being expressed only in the swarmer pole of the predivisional cell. The only 54 activator described so far is the FlbD protein, which is involved in activation of the class III and IV flagellar genes and repression of the fliF promoter. To identify new roles for 54 in the metabolism and differentiation of C. crescentus, we cloned and characterized a gene encoding a putative 54 activator, named tacA. The deduced amino acid sequence from tacA has high similarity to the proteins from the NtrC family of transcriptional activators, including the aspartate residues that are phosphorylated by histidine kinases in other activators. The promoter region of the tacA gene contains a conserved sequence element present in the promoters of class II flagellar genes, and tacA shows a temporal pattern of expression similar to the patterns of these genes. We constructed an insertional mutant that is disrupted in tacA (strain SP2016), and an analysis of this strain showed that it has all polar structures, such as pili, stalk, and flagellum, and displays a motile phenotype, indicating that tacA is not involved in the flagellar biogenesis pathway. However, this strain has a high percentage of filamentous cells and shows a clear-plaque phenotype when infected with phage Cb5. These results suggest that the TacA protein could mediate the effect of 54 on a different pathway in C. crescentus.The Caulobacter crescentus cell cycle has a precisely controlled differentiation program in which two dissimilar daughter cells, a motile swarmer cell and a sessile stalked cell, are generated at every round of cell division (for reviews, see references 8 and 22). The coordination of all steps involved in these morphological changes is still poorly understood, but genetic evidence shows that stalk and flagellum biogenesis are related to cell division and chromosome replication (7,13,48,52).The most extensively studied process in Caulobacter differentiation is flagellum biogenesis. Expression of flagellar genes in the predivisional cell is cell cycle regulated and is subjected to a complex regulatory hierarchy. The first set of genes to be expressed (class II genes) is absolutely required for the expression of class III and IV genes, which code for the most external flagellar structures. Several strains with mutations in class II genes have been isolated, and all show a nonmotile phenotype as well as defects in cell division (7,12,24,59).The class II genes are all transcribed at the same time during the cell cycle, being expressed in the early predivisional cell, before any of the class III genes are expressed. The promoter sequences of some of the class II genes have been described and show a conserved element between positions Ϫ40 to Ϫ20 relative to the start site of transcription that is distinct from the consensus promoter sequences for Caulobacter 70 and 54 (3,12,4...

The dynamic interplay between a cell fate determinant and a lysozyme homolog drives the asymmetric division cycle of Caulobacter crescentus

“…Previous experiments implicated that tacA transcription is under the control of CtrA (Marques et al 1997), suggesting that ⌬pleC cells might be unable to activate spmX transcription because they lack sufficient amounts of TacA. As expected, immunoblotting revealed that TacA levels are markedly reduced in extracts from ⌬pleC and ctrA401 cells compared with those from wild-type cells (Fig.…”

“…6E). The tacA promoter features a CtrA box that overlaps the −35 promoter motif (Marques et al 1997), providing further support for the hypothesis that a decrease in CtrA∼P is responsible for the reduction of TacA in ⌬pleC cells. Whether or not CtrA binds the tacA promoter in vivo is unknown.…”

“…6D; McGrath et al 2007). E 54 -catalyzed transcription normally requires a coactivator of a specialized clade of response regulators (Popham et al 1989), of which there are only four encoded in the Caulobacter genome and TacA is one of them (Marques et al 1997). Immunoblot analysis and P spmX -lacZ reporter assays were used to test if TacA regulates spmX expression.…”

A CysB-regulated and σ54-dependent regulator, SfnR, is essential for dimethyl sulfone metabolism of Pseudomonas putida strain DS1

“…B64992; Canellakis et al, 1993), and TacA (34 %) from Caulobacter crescentus (accession no. AAC45640; Marques et al, 1997). The sequence alignment of SfnR with these response regulators demonstrated that SfnR had the central ATP-dependent s 54 factor (RpoN) interaction domain and the C-terminal helix-turn-helix DNA-binding domain.…”

In-phase oscillation of global regulons is orchestrated by a pole-specific organizer

“…The active and phosphorylated form of TacA (TacA∼P) controls stalk biogenesis, by acting on a subclass of σ 54 -dependent genes (17,22). Although the TacA regulon remains uncharted on a genome-wide scale, it is known Significance Although several studies have pointed towards the importance of the sigma factor, σ 54 , in regulating virulence, biofilm formation, and cell cycle control in α-proteobacteria, knowledge on its activators and their regulation is incomplete.…”