Identification of a gene encoding a thioredoxin-like product necessary for cytochrome c biosynthesis and symbiotic nitrogen fixation in Rhizobium leguminosarum.
A Tn5-induced mutant of Rhizobium leguminosarum bv. viciae could not form nitrogen-fixing nodules on pea or vetch because of a lesion in electron transport to oxygen. The mutant lacked spectroscopically detectable cytochromes c and aa3. No proteins containing c-type cytochrome could be identified in the mutant by heme staining of proteins fractionated on polyacrylamide gels, indicating that the mutant was defective in maturation of all c-type cytochromes. The Tn5 mutation was determined to be located in a gene that was called cycY. The cycY gene product is homologous to the thioredoxin-like protein HelX involved in the assembly of c-type cytochromes in Rhodobacter capsulatus and to an open reading frame from a Bradyrhizobium japonicum gene cluster containing other genes involved in cytochrome c biogenesis. Our observations are consistent with CycY functioning as a thioredoxin that reduces cysteine residues in apocytochromes c before heme attachment.
John Innes Institute, Norwich, United Kingdom.
C
C
Vargas
G
G
Wu
A E
AE
Davies
J A
JA
Downie
D000595:Amino Acid Sequence; D001483:Base Sequence; D002248:Carbon Monoxide / Q000378:metabolism; D003574:Cytochrome c Group / Q000096:biosynthesis* / Q000737:chemistry / Q000235:genetics*; D003576:Electron Transport Complex IV / Q000032:analysis; D005798:Genes, Bacterial / Q000235:genetics*; D008027:Light; D008969:Molecular Sequence Data; D009586:Nitrogen Fixation / Q000235:genetics; D010101:Oxygen Consumption / Q000235:genetics; D016961:Rhizobium leguminosarum / Q000235:genetics*; D017386:Sequence Homology, Amino Acid; D013053:Spectrophotometry; D013559:Symbiosis; D013879:Thioredoxins / Q000235:genetics*
D003574:Cytochrome c Group; C080693:cytochrome Cy; D013879:Thioredoxins; D002248:Carbon Monoxide; D003576:Electron Transport Complex IV