Elucidation of expression/regulation of genes involved in microbial polyhydroxylalkanoate (PHA)

为了阐明嗜热菌和甲基营养菌Paracoccus ficans合成/降解PHA的调控机制，本论文从基因/酶/代谢水平进行了研究，主要研究内容如下：1.在phaP的下游发现了一个名为phaR的基因，该基因编码PHA颗粒相关蛋白，相蛋白。PhaR是一个转录因子，它与phaP的启动子区结合，也与PHA颗粒结合。调节PHA颗粒大小. PHA合成/降解相关基因phaA、phaB、phaC和phaZ的表达与PHA合成水平无关，代谢产物辅酶A被认为是PHA生物合成的全局调节因子.对三种参与PHA胞内降解的酶，即两种不同类型的PHA解聚酶和PHB寡聚物水解酶进行了纯化，并阐明了它们的生化特性。其中一种PHA解聚酶是一种新的酶，它可以直接从聚羟基丁酸酯聚合物中产生3-羟基丁酸酯单体。

With aim of elucidating regulation mechanism of PHA synthesis/degradation within denitrifyer and methylotroph, Paracoccus denitrificans, studies were carried out on genes/enzymes/metabolism levels, and the following have been achieved.1. A gene named phaR, was discovered downstream of phaP that encoded PHA granule-associated protein, phasin. PhaR was a transcription factor which bound promoter region of phaP and also bound the PHA granule. It regulated the size of PHA granule.2. Genes involved in PHA synthesis/degradation, i.e phaA, phaB, phaC, and phaZ, were expressed almost constitutively irrespective of PHA synthesis level.A metabolite, Coenzyme A, was proposed as a global regulator of PHA biosynthesis.3. Three enzymes involved in the intracellular degradation of PHA, i.e. two different kinds of PHA depolymerases, and PHB oligomer hydrolase, were purified and their biochemical characteristics were elucidated. One of the PHA depolymerases was a novel enzyme which yielded 3-hydroxylbutyrate monomer directly from PHB polymer.