Aichi Makiko, Yoshihara Saori, Yamashita Madoka, Maeda Shin-ichi, Nagai Kazuo, Omata Tatsuo
Department of Biological Chemistry, Chubu University, Kasugai, Japan.
Biosci Biotechnol Biochem. 2006 Nov;70(11):2682-9. doi: 10.1271/bbb.60286. Epub 2006 Nov 7.
The products of the NpR1527 and NpR1526 genes of the filamentous, diazotrophic, fresh-water cyanobacterium Nostoc punctiforme strain ATCC 29133 were identified as a nitrate transporter (NRT) and nitrate reductase (NR) respectively, by complementation of nitrate assimilation mutants of the cyanobacterium Synechococcus elongatus strain PCC 7942. While other fresh-water cyanobacteria, including S. elongatus, have an ATP-binding cassette (ABC)-type NRT, the NRT of N. punctiforme belongs to the major facilitator superfamily, being orthologous to the one found in marine cyanobacteria (NrtP). Unlike the ABC-type NRT, which transports both nitrate and nitrite with high affinity, Nostoc NrtP transported nitrate preferentially over nitrite. NrtP was distinct from ABC-type NRT also in its insensitivity to ammonium-promoted regulation at the post-translational level. The nitrate reductase of N. punctiforme was, on the other hand, inhibited upon addition of ammonium to medium, lending ammonium sensitivity to nitrate assimilation.
通过对细长聚球藻菌株PCC 7942的硝酸盐同化突变体进行互补，丝状、固氮淡水蓝藻点状念珠藻菌株ATCC 29133的NpR1527和NpR1526基因产物分别被鉴定为硝酸盐转运蛋白（NRT）和硝酸盐还原酶（NR）。虽然包括细长聚球藻在内的其他淡水蓝藻具有ATP结合盒（ABC）型NRT，但点状念珠藻的NRT属于主要转运蛋白超家族，与海洋蓝藻中发现的一种NRT（NrtP）直系同源。与高亲和力转运硝酸盐和亚硝酸盐的ABC型NRT不同，点状念珠藻NrtP优先转运硝酸盐而非亚硝酸盐。NrtP在翻译后水平对铵促进调节不敏感方面也与ABC型NRT不同。另一方面，向培养基中添加铵会抑制点状念珠藻的硝酸盐还原酶，使硝酸盐同化对铵敏感。
