Departamento de Microbiología Molecular, Instituto de Biotecnología, Universidad Nacional Autónoma de México, Avenida Universidad 2001, Col. Chamilpa, CP 62210 Cuernavaca, Morelos, México.
Centro de Investigaciones en Ciencias Microbiológicas, Instituto de Ciencias, Benemérita Universidad Autónoma de Puebla, Apartado Postal 1622, CP 72000 Puebla, México.
Microbiology (Reading). 2012 Aug;158(Pt 8):1953-1963. doi: 10.1099/mic.0.059329-0. Epub 2012 May 18.
In Azotobacter vinelandii the two-component GacS/GacA system is required for synthesis of polyhydroxybutyrate (PHB) and of the exopolysaccharide alginate. The RsmA protein was shown to interact with the alginate biosynthetic algD mRNA, acting as a translational repressor, and GacA was found to activate transcription of the rsmZ1 and rsmZ2 genes that encode small RNAs interacting with RsmA to counteract its repressor activity. The phbBAC operon encodes the enzymes of PHB synthesis and is activated by the transcriptional regulator PhbR. This study shows that GacA is required for transcription of one rsmY and seven rsmZ1-rsmZ7 genes present in the A. vinelandii genome, and that inactivation of rsmA results in increased PHB production. Transcriptional and translational phbR-gusA gene fusions were used to show that the gacA mutation negatively affected the expression of the phbR gene at the translational level. We also demonstrated an in vitro interaction of RsmA with RNAs corresponding to phbB and phbR mRNA leaders, and showed that the stability of phbR and phbB mRNAs is increased in the rsmA mutant. Taken together these results indicate that in A. vinelandii, RsmA post-transcriptionally represses the expression of PhbR.
在固氮菌中，双组分 GacS/GacA 系统是合成聚羟基丁酸酯 (PHB) 和胞外多糖海藻酸盐所必需的。RsmA 蛋白被证明与海藻酸盐生物合成 algD mRNA 相互作用，作为翻译抑制剂，而 GacA 被发现激活编码与 RsmA 相互作用的小 RNA rsmZ1 和 rsmZ2 基因的转录，以抵消其抑制活性。phbBAC 操纵子编码 PHB 合成酶，由转录调节因子 PhbR 激活。本研究表明，GacA 是在土壤杆菌基因组中存在的一个 rsmY 和七个 rsmZ1-rsmZ7 基因转录所必需的，而 rsmA 的失活导致 PHB 产量增加。转录和翻译 phbR-gusA 基因融合用于表明 gacA 突变在翻译水平上对 phbR 基因的表达产生负面影响。我们还证明了 RsmA 与对应于 phbB 和 phbR mRNA 前导序列的 RNA 之间的体外相互作用，并表明 rsmA 突变体中 phbR 和 phbB mRNA 的稳定性增加。这些结果表明，在固氮菌中，RsmA 在后转录水平上抑制 PhbR 的表达。
