title: The phzA2-G2 transcript exhibits direct RsmA-mediated activation in Pseudomonas aeruginosa M18.
abstract: In bacteria, RNA-binding proteins of the RsmA/CsrA family act as post-transcriptional regulators that modulate translation initiation at target transcripts. The Pseudomonas aeruginosa genome contains two phenazine biosynthetic (phz) gene clusters, phzA1-G1 (phz1) and phzA2-G2 (phz2), each of which is responsible for phenazine-1-carboxylic acid (PCA) biosynthesis. In the present study, we show that RsmA exhibits differential gene regulation on two phz clusters in P. aeruginosa M18 at the post-transcriptional level. Based on the sequence analysis, four GGA motifs, the potential RsmA binding sites, are found on the 5'-untranslated region (UTR) of the phz2 transcript. Studies with a series of lacZ reporter fusions, and gel mobility shift assays suggest that the third GGA motif (S3), located 21 nucleotides upstream of the Shine-Dalgarno (SD) sequence, is involved in direct RsmA-mediated activation of phz2 expression. We therefore propose a novel model in which the binding of RsmA to the target S3 results in the destabilization of the stem-loop structure and the enhancement of ribosome access. This model could be fully supported by RNA structure prediction, free energy calculations, and nucleotide replacement studies. In contrast, various RsmA-mediated translation repression mechanisms have been identified in which RsmA binds near the SD sequence of target transcripts, thereby blocking ribosome access. Similarly, RsmA is shown to negatively regulate phz1 expression. Our new findings suggest that the differential regulation exerted by RsmA on the two phz clusters may confer an advantage to P. aeruginosa over other pseudomonads containing only a single phz cluster in their genomes.
authors.affiliation: SKLMM of Life Sciences and Biotechnology School, Shanghai Jiao Tong University, Shanghai, People's Republic of China.
authors.forename: Bin
authors.initials: B
authors.lastname: Ren
authors.affiliation: SKLMM of Life Sciences and Biotechnology School, Shanghai Jiao Tong University, Shanghai, People's Republic of China.
authors.forename: Huifeng
authors.initials: H
authors.lastname: Shen
authors.affiliation: MOE Key Laboratory of Bioinformatics, School of Life Sciences, Tsinghua University, Beijing, People's Republic of China.
authors.forename: Zhi John
authors.initials: ZJ
authors.lastname: Lu
authors.affiliation: SKLMM of Life Sciences and Biotechnology School, Shanghai Jiao Tong University, Shanghai, People's Republic of China.
authors.forename: Haiming
authors.initials: H
authors.lastname: Liu
authors.affiliation: SKLMM of Life Sciences and Biotechnology School, Shanghai Jiao Tong University, Shanghai, People's Republic of China.
authors.forename: Yuquan
authors.initials: Y
authors.lastname: Xu
mesh_terms: D020121:5' Untranslated Regions / Q000235:genetics; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D001483:Base Sequence; D015964:Gene Expression Regulation, Bacterial; D008969:Molecular Sequence Data; D009876:Operon; D010619:Phenazines / Q000378:metabolism; D011550:Pseudomonas aeruginosa / Q000235:genetics* / Q000378:metabolism; D016601:RNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*
chemical_list: D020121:5' Untranslated Regions; D001426:Bacterial Proteins; D010619:Phenazines; D016601:RNA-Binding Proteins; C037165:1-phenazinecarboxylic acid