Saito Akihiro, Ishizaka Masumi, Francisco Perigio B, Fujii Takeshi, Miyashita Kiyotaka
National Institute of Agro-Environmental Sciences, Kan-nondai 3-1-1, Tsukuba, Ibaraki 305-8604, Japan1.
Microbiology (Reading). 2000 Nov;146 ( Pt 11):2937-2946. doi: 10.1099/00221287-146-11-2937.
Streptomyces coelicolor A3(2) strain M145 has eight chitinase genes scattered on the chromosome: six genes for family 18 (chiA, B, C, D, E and H) and two for family 19 (chiF and G). In this study, the expression and regulation of these genes were investigated. The transcription of five of the genes (chiA, B, C, D and F) was induced in the presence of colloidal chitin while that of the other three genes (chiE, G and H) was not. The transcripts of the five induced chi genes increased and reached their maximum at 4 h after the addition of colloidal chitin, all showing the same temporal patterns. The induced levels of the transcripts of chiB were significantly lower than those of the other four genes. Dynamic analysis of the transcripts of the chi genes indicated that chiA and chiC were induced more strongly than chiD and chiF. Addition of chitobiose also induced transcription of the chi genes, but significantly earlier than did colloidal chitin. When cells were cultured in the presence of colloidal chitin, an exponential increase of chitobiose concentration in the culture supernatant was observed prior to the induced transcription of the chi genes. This result, together with the immediate effect of chitobiose on the induction, suggests that chitobiose produced from colloidal chitin is involved in the induction of transcription of the chi genes. The transcription of the five chi genes was repressed by glucose. This repression was apparently mediated by the glucose kinase gene glkA.
天蓝色链霉菌A3(2)菌株M145在染色体上分散有8个几丁质酶基因：6个属于18家族的基因（chiA、B、C、D、E和H）以及2个属于19家族的基因（chiF和G）。在本研究中，对这些基因的表达和调控进行了研究。其中5个基因（chiA、B、C、D和F）的转录在胶体几丁质存在时被诱导，而其他3个基因（chiE、G和H）则未被诱导。5个被诱导的chi基因的转录本在添加胶体几丁质后增加，并在4小时达到最大值，均呈现相同的时间模式。chiB转录本的诱导水平显著低于其他4个基因。对chi基因转录本的动态分析表明，chiA和chiC的诱导程度强于chiD和chiF。添加壳二糖也诱导chi基因的转录，但比胶体几丁质早得多。当细胞在胶体几丁质存在下培养时，在chi基因诱导转录之前，观察到培养上清液中壳二糖浓度呈指数增加。这一结果以及壳二糖对诱导的即时作用表明，由胶体几丁质产生的壳二糖参与了chi基因转录的诱导。5个chi基因的转录受到葡萄糖的抑制。这种抑制显然是由葡萄糖激酶基因glkA介导的。
