MOLYBDENUM COFACTOR BIOSYNTHESIS - THE ARABIDOPSIS-THALIANA CDNA CNX1ENCODES A MULTIFUNCTIONAL 2-DOMAIN PROTEIN HOMOLOGOUS TO A MAMMALIAN NEUROPROTEIN, THE INSECT PROTEIN CINNAMON AND 3 ESCHERICHIA-COLI PROTEINS

The molybdenum co-factor (Moco) is an essential part of all eukaryotic molybdoenzymes. It is a molybdopterin and reveals the same principal structure in eubacteria, archaebacteria and eukaryotes. This paper rep orts the isolation of cnx1, a cDNA clone of Arabidopsis thaliana which complements the Escherichia coli Moco mutant mogA. The mapping data o f this cDNA correlate well with the mapping position of the A. thalian a molybdenum cofactor locus chl6. As mutants in chl6 are known to be r epairable by high concentrations of molybdate, the defective gene is v ery likely to be involved in the last step of Moco biosynthesis, that is, the insertion of molybdenum into molybdopterin. The protein encode d by cnx1 shows a two-domain structure: the N-terminal domain is homol ogous to the E. coli Moco protein MoeA, the C-terminal domain is homol ogous to the E. coli Moco proteins MoaB and MogA, respectively. These homologies show that part of the prokaryotic Moco biosynthetic pathway accomplished by monofunctional proteins in E. coli, is performed by a single multifunctional protein in eukaryotes. In addition Cnx1 is hom ologous to the eukaryotic proteins Gephyrin, a rat neuroprotein, and C innamon, a Drosophila protein with a function in Moco biosynthesis. Th ese proteins also show a two-domain structure but the order of the dom ains is inversed as compared with Cnx1. Southern analysis indicates th e existence of at least one further member, in addition to the cnx1 ge ne, of this novel gene family in the Arabidopsis genome.