Study on Two-Component Signal Transduction System in an Intracellular Symbiotic Bacterium

共生蛋白（Symbionin）是蚜虫胞内共生细菌Buchnera产生的GroEL同源分子伴侣蛋白，它不仅是一种分子伴侣蛋白，而且是一种新型的磷载体蛋白，这表明该蛋白在细胞内环境下的细菌特有的信号转导系统中起着关键作用。这促使我对双组分信号转导系统中的“传感器分子或组氨酸蛋白激酶（HPK）”和磷酸转移酶系统（PTS）中的“含组氨酸磷载体蛋白（HPR）”等可能与其他自由生活细菌共有的Buchnera磷酸载体蛋白进行了研究，得到了以下结果。一种能够接受磷酸化共生素磷酸化部分的25 kda蛋白被鉴定为组蛋白H1。Buchnera组蛋白H1是用5% PCA提取的真核组蛋白，同样保留了dna结合活性。克隆了Buchnera组蛋白H1基因，并根据其核苷酸序列推断出其完整的氨基酸序列。这是首次报道的原核组蛋白H1。相比之下，没有证据表明在布氏菌中存在双组分系统的传感器激酶，这些激酶通常存在于许多自由生活的细菌中。这可能是布氏菌基因组中传感器激酶的缺乏被这种共生细菌中的多功能共生素所补偿。我成功鉴定了ptsH-ptsl-ccr，并提供了这三个基因在Buchnera细胞中活跃表达的证据。此外，研究还表明，“I酶”可以被磷酸烯醇丙酮酸（PEP）自催化磷酸化，而不能被ATP自催化磷酸化，这表明磷酸转移酶系统（PTS）在Buchnera细胞中也起着积极的作用。

Symbionin, a GroEL homologous molecular chaperone produced by Buchnera, an intracellular symbiotic bacterium of aphids, is not only a molecular chaperone but also a novel phosphocarrier protein, suggesting that this protein plays a key role in 'the signal transducing system specific to the bacterium living in an intracellular environment. This promoted me to look into Buchnera phosphocarrier proteins such as "sensor molecule or histidine protein kinase (HPK)" of the two-component signal transducing system and "histidine-containing phosphocarrier protein (HPR) " of phosphotransferase system (PTS) that may be shared in common with other free-living bacteria, and the following results were obtained.1. A 25-kDa protein that is able to accept the phosphoryl moiety of phosphorylated symbionin was identified as histone H1. Buchnera histone H1 is extracted with 5% PCA like eukaryotic histones and also retains the DNA-binding activity. The gene for Buchnera histone H1 was cloned and the full amino acid sequence was deduced from its nucleotide sequence. This is the first report of the prokaryotic histone H1. In contrast, no evidence was obtained for the presence of sensor kinases of the two-component system in Buchnera, which are generally found in many free-living bacteria. It is possible that the lack of sensor kinases in Buchnera genome is compensated for by multifunctional symbionin in this symbiotic bacterium.2. I successfully identified ptsH-ptsl-ccr and provide the evidence that these three genes are actively expressed in Buchnera cells. Also, it was demonstrated that "Enzyme I" is auto-catalytically phopshorylated by phosphoenolpyruvate (PEP), but not by ATP, suggesting that phosphotransferase system (PTS) is also actively functioning in Buchnera cells.