title: A modular domain of NifU, a nitrogen fixation cluster protein, is highly conserved in evolution.
abstract: hnifU, a gene exhibiting similarity to nifU genes of nitrogen fixation gene clusters, was identified in the course of expressed sequence tag (EST) generation from a human fetal heart cDNA library. Northern blot of human tissues and polymerase chain reaction (PCR) using human genomic DNA verified that the hnifU gene represented a human gene rather than a microbial contaminant of the cDNA library. Conceptual translation of the hnifU cDNA yielded a protein product bearing 77% and 70% amino acid identity to NifU-like hypothetical proteins from Haemophilus influenzae and Saccharomyces cerevisiae, respectively, and 40-44% identity to the N-terminal regions of NifU proteins from several diazatrophs (i.e., nitrogen-fixing organisms). Pairwise determination of amino acid identities between the NifU-like proteins of nondiazatrophs showed that these NifU-like proteins exhibited higher sequence identity to each other (63-77%) than to the diazatrophic NifU proteins (40-48%). Further, the NifU-like proteins of non-nitrogen-fixing organisms were similar only to the N-terminal region of diazatrophic NifU proteins and therefore identified a novel modular domain in these NifU proteins. These findings support the hypothesis that NifU is indeed a modular protein. The high degree of sequence similarity between NifU-like proteins from species as divergent as humans and H. influenzae suggests that these proteins perform some basic cellular function and may be among the most highly conserved proteins.
authors.affiliation: Department of Clinical Biochemistry, The Centre for Cardiovascular Research, The Toronto Hospital, University of Toronto, Canada.
authors.forename: D M
authors.initials: DM
authors.lastname: Hwang
authors.forename: A
authors.initials: A
authors.lastname: Dempsey
authors.forename: K T
authors.initials: KT
authors.lastname: Tan
authors.forename: C C
authors.initials: CC
authors.lastname: Liew
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000235:genetics*; D001483:Base Sequence; D003001:Cloning, Molecular; D017124:Conserved Sequence / Q000235:genetics*; D018076:DNA, Complementary / Q000235:genetics*; D005318:Fetal Heart; D015870:Gene Expression; D005796:Genes / Q000235:genetics; D006801:Humans; D007506:Iron-Sulfur Proteins; D008969:Molecular Sequence Data; D009206:Myocardium / Q000737:chemistry; D009586:Nitrogen Fixation / Q000235:genetics; D009928:Organ Specificity; D011506:Proteins / Q000235:genetics*; D012333:RNA, Messenger / Q000032:analysis; D016415:Sequence Alignment; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid; D012689:Sequence Homology, Nucleic Acid
chemical_list: D001426:Bacterial Proteins; D018076:DNA, Complementary; C506160:ISCU protein, human; D007506:Iron-Sulfur Proteins; C088637:NifU protein, Bacteria; D011506:Proteins; D012333:RNA, Messenger