D'hooghe I, Michiels J, Vlassak K, Verreth C, Waelkens F, Vanderleyden J
F. A. Janssens Laboratory of Genetics, Catholic University of Leuven, Heverlee, Belgium.
Mol Gen Genet. 1995 Nov 1;249(1):117-26. doi: 10.1007/BF00290243.
The fixLJ genes of Rhizobium leguminosarum biovar phaseoli CNPAF512 were identified by DNA hybridization of a genomic library with an internal fragment of the Rhizobium meliloti fixJ gene. The nucleotide sequence was determined and the corresponding amino acid sequence was aligned with the amino acid sequences of the FixL proteins of R. meliloti, Bradyrhizobium japonicum and Azorhizobium caulinodans. While the FixJ protein and the carboxy-terminal part of the FixL protein are highly homologous to the other FixL and FixJ proteins, the homology in the central heme-binding, oxygen-sensing domain and in the amino-terminal domain of FixL is very low. The R. leguminosarum bv. phaseoli FixL protein does not contain the heme-binding motif defined for the previously described FixL proteins. R. leguminosarum bv. phaseoli fixLJ and fixJ mutants were constructed. These mutants can still fix nitrogen, albeit at a reduced level. Expression analysis of nifA-gusA and nifH-gusA fusions in the constructed mutants revealed that the R. leguminosarum bv. phaseoli fixLJ genes are involved in microaerobic nifH expression but not in nifA expression.
用苜蓿根瘤菌fixJ基因的内部片段对菜豆根瘤菌生物变种CNPAF512的基因组文库进行DNA杂交，从而鉴定出了菜豆根瘤菌的fixLJ基因。测定了其核苷酸序列，并将相应的氨基酸序列与苜蓿根瘤菌、大豆慢生根瘤菌和茎瘤固氮根瘤菌的FixL蛋白的氨基酸序列进行了比对。虽然FixJ蛋白和FixL蛋白的羧基末端部分与其他FixL和FixJ蛋白高度同源，但FixL蛋白的中央血红素结合、氧感应结构域和氨基末端结构域的同源性非常低。菜豆根瘤菌生物变种的FixL蛋白不包含为先前描述的FixL蛋白定义的血红素结合基序。构建了菜豆根瘤菌生物变种的fixLJ和fixJ突变体。这些突变体仍然能够固氮，尽管固氮水平有所降低。对构建的突变体中nifA - gusA和nifH - gusA融合体的表达分析表明，菜豆根瘤菌生物变种的fixLJ基因参与微需氧条件下nifH的表达，但不参与nifA的表达。
