A novel signal transduction system involved in osmotic adjustment in Myxococcus xanthus.

从黄粘球菌中分离到两个腺苷酸环化酶基因cyaA和cyaB。预测的cyaA和cyaB基因产物与受体型腺苷酸环化酶具有结构相似性，受体型腺苷酸环化酶由腺苷酸环化酶的氨基端传感器结构域和羧基端催化结构域组成。在高离子（NaCl）或高非离子（蔗糖）渗透胁迫下，cyaA突变体的孢子形成和孢子萌发明显减少。在营养细胞中，cyaA突变体对渗透胁迫反应正常。另一方面，cyaB的破坏产生的突变体在高离子（NaCl）或高非离子（蔗糖）渗透压下表现出生长迟缓。在非离子渗透胁迫下，cyaB突变体孢子萌发率降低，但cyaB突变体的萌发率显著高于cyaA突变体。这些结果表明，黄原菌CyaA和CyaB主要在黄原菌的发育和孢子萌发过程中起渗透感受器的作用，而CyaA和CyaB分别在黄原菌的整个生命周期中起渗透感受器的作用，包括营养期。接下来，我们利用基于camp依赖性蛋白激酶（PKA）调控亚基的保守camp结合结构域设计的寡核苷酸探针，从M. xanthus基因组DNA文库中分离出一个克隆。该克隆包含一个开放阅读框架cbpB，编码一个具有两个camp结合域的亲水性蛋白。CbpB与PKA调控亚基具有部分初级结构相似性。cbpB突变体生长发育正常，孢子萌发正常。然而，在高温或低温条件下培养的cbpB突变体的生长明显下降。cbpB突变细胞对渗透胁迫的敏感性也高于野生型细胞。cbpB突变体的表型与某些真核微生物的PKA调控亚基突变体相似。这些结果表明，camp介导的信号转导通路在黄原草的渗透和温度适应中起着重要作用。camp介导的信号转导途径在细菌中未见报道。少

Two adenylyl cyclase genes (cyaA and cyaB) were isolated from Myxococcus xanthus. The predicted cyaA and cyaB gene products had structural similarity to the receptor-type adenylyl cyclases that are composed of an amino-terminal sensor domain and a carboxy-terminal catalytic domain of adenylyl cyclase. A cyaA mutant, placed under condition of high-ionic (NaCl) or high-nonionic (sucrose) osmostress exhibited a marked reduction in spore formation and spore germination. In vegetative cells, cyaA mutant responded normally to osmotic stress. On the other hand, disruption of cyaB generates a mutant that showed growth retardation at high-ionic (NaCl) or high-nonionic (sucrose) osmolarity. Under nonionic osmostress, the cyaB mutant exhibited reduced spore germination, however, the germination rate of the cyaB mutant was significantly higher than that of the cyaA mutant. These results suggested that M. xanthus CyaA and CyaB function as osmosensors mainly during development and spore germination, … More and throughout the life cycle of M. xanthus including the vegetative stage, respectively.Next, we isolated a clone from a M. xanthus genomic DNA library using oligonucleotide probes designed based on the conserved cAMP-binding domains of the cAMP-dependent protein kinase (PKA) regulatory subunits. The clone contained an open-reading frame, cbpB, encoding a hydrophilic protein with two cAMP-binding domains. The CbpB exhibited partial primary structural similarity to PKA regulatory subunits. cbpB mutant showed normal growth, development and spore germination. However, the cbpB mutant cultured under high- or low-temperature conditions exhibited a marked reduction in growth. cbpB mutant cells were also more sensitive to osmotic stress than wild-type cells. The phenotype of cbpB mutant was similar to those of PKA regulatory subunit mutants of some eukaryotic microorganisms. These results suggest that the cAMP-mediated signal transduction pathway plays an important role in osmotic and temperature adaptation in M. xanthus. The cAMP-mediated signal transduction pathway is not reported in bacteria. Less