Department of Botany, The Hebrew University of Jerusalem, 91904 Jerusalem, Israel.
Plant Physiol. 1992 Dec;100(4):1987-93. doi: 10.1104/pp.100.4.1987.
The high CO(2)-requiring mutants of Synechococcus PCC 7942, D4 and R14, were obtained by deletion or inactivation (respectively) of an open reading frame immediately downstream of rbc (the operon encoding the subunits of ribulose 1,5-bisphosphate carboxylase/oxygenase). These mutants exhibit photosynthetic characteristics similar to those of high CO(2)-grown wild type, unlike other cyanobacterial high CO(2)-requiring mutants, where the apparent photosynthetic affinity for inorganic carbon is approximately 2 orders of magnitude lower than that of the wild type. Sequence analysis and metabolic complementation of the mutants by inosine 5'-monophosphate identified this open reading frame as the cyanobacterial equivalent of purK, the eubacterial gene encoding subunit II of phosphoribosyl aminoimidazole carboxylase in the purine biosynthetic pathway. Exposure of high CO(2)-grown Synechococcus to low CO(2) conditions led to the induction of transcription of purK. It is suggested that the high CO(2)-requiring phenotype of these mutants resulted from the defect in purine biosynthesis after exposure to low CO(2). We also raise the possibility that the level of cellular purines is involved in the process of adaptation of cyanobacteria to low concentrations of CO(2).
聚球藻 PCC 7942 的高 CO2 需求突变体 D4 和 R14 是通过缺失或失活（分别）位于 rbc 下游的一个开放阅读框获得的（该操纵子编码核酮糖 1,5-二磷酸羧化酶/加氧酶的亚基）。与其他蓝藻高 CO2 需求突变体不同，这些突变体表现出与高 CO2 生长的野生型相似的光合作用特征，在其他蓝藻高 CO2 需求突变体中，无机碳的表观光合作用亲和力比野生型低约 2 个数量级。通过肌苷 5'-单磷酸对突变体的序列分析和代谢互补鉴定出这个开放阅读框是蓝藻 purK 的等效物，purK 是编码嘌呤生物合成途径中磷酸核糖基氨基咪唑羧化酶亚基 II 的原核生物基因。将高 CO2 生长的聚球藻暴露在低 CO2 条件下会导致 purK 的转录诱导。这表明这些突变体的高 CO2 需求表型是由于暴露在低 CO2 条件下嘌呤生物合成的缺陷所致。我们还提出了这样一种可能性，即细胞内嘌呤的水平可能参与了蓝藻适应低浓度 CO2 的过程。
