Borgia P T
Department of Medical Microbiology and Immunology, School of Medicine, Southern Illinois University, Springfield 62794-9230.
J Bacteriol. 1992 Jan;174(2):384-9. doi: 10.1128/jb.174.2.384-389.1992.
Strains of Aspergillus nidulans carrying the orlA1 or tse6 allele are deficient in cell wall chitin and undergo lysis at restrictive temperatures. The strains are remediable by osmotic stabilizers or by the presence of N-acetylglucosamine (GlcNAc) in the medium. The remediation by GlcNAc suggests that the lesion(s) in chitin synthesis resides in the amino sugar biosynthetic pathway prior to the synthesis of N-acetylglucosamine-6-phosphate. orlA1 strains grown at permissive temperature exhibit an abnormally low specific activity for L-glutamine:fructose-6-phosphate amidotransferase (EC 2.6.1.16, amidotransferase), the first enzyme unique to amino sugar synthesis. In addition, the enzyme produced is temperature sensitive in vitro. tsE6 strains grown at permissive temperature show virtually no amidotransferase activity. This finding is consistent with an extremely labile enzyme which is destroyed by cell breakage and extract preparation. The enzyme must be active in vivo at permissive temperatures since GlcNAc is not required for growth. Thus, two structural genes (orlA and tsE) are necessary for the amidotransferase activity. bimG11 strains are temperature sensitive for a type 1 protein phosphatase involved in cell cycle regulation and arrest in mitosis. Like orlA1 and tsE6 strains, conidia from bimG11 strains swell excessively when germinated and lyse; the germlings produced are deficient in chitin content. The amidotransferase from wild-type and mutant strains is sensitive to feedback inhibition by uridine diphosphate-N-acetylglucosamine. The sensitivity of the amidotransferase from bimG11 strains is dependent on growth temperature, while that from wild-type strains is independent of temperature. The enzyme can be desensitized in vitro under conditions consistent with a protein phosphatase reaction. It is proposed that amino sugar (and chitin biosynthesis) is partially regulated by phosphorylation-dephosphorylation of the amidotransferase or a protein regulator of the enzyme.
携带orlA1或tse6等位基因的构巢曲霉菌株细胞壁几丁质缺乏，在限制温度下会发生裂解。这些菌株可通过渗透稳定剂或培养基中存在的N-乙酰葡糖胺（GlcNAc）进行补救。GlcNAc的补救作用表明，几丁质合成中的损伤存在于N-乙酰葡糖胺-6-磷酸合成之前的氨基糖生物合成途径中。在允许温度下生长的orlA1菌株对L-谷氨酰胺：果糖-6-磷酸酰胺转移酶（EC 2.6.1.16，酰胺转移酶）表现出异常低的比活性，该酶是氨基糖合成中独特的第一种酶。此外，所产生的酶在体外对温度敏感。在允许温度下生长的tsE6菌株几乎没有酰胺转移酶活性。这一发现与一种极易失活的酶一致，该酶会被细胞破碎和提取物制备过程破坏。由于生长不需要GlcNAc，该酶在允许温度下必须在体内具有活性。因此，酰胺转移酶活性需要两个结构基因（orlA和tsE）。bimG11菌株对参与细胞周期调控并在有丝分裂中停滞的1型蛋白磷酸酶对温度敏感。与orlA1和tsE6菌株一样，bimG11菌株的分生孢子在萌发时过度膨胀并裂解；所产生的芽管几丁质含量不足。来自野生型和突变菌株的酰胺转移酶对尿苷二磷酸-N-乙酰葡糖胺的反馈抑制敏感。来自bimG11菌株的酰胺转移酶的敏感性取决于生长温度，而来自野生型菌株的敏感性与温度无关。该酶在与蛋白磷酸酶反应一致的条件下可在体外脱敏。有人提出，氨基糖（和几丁质生物合成）部分受酰胺转移酶或该酶的蛋白调节剂的磷酸化-去磷酸化调节。
