Three different genes encode NM23/nucleoside diphosphate kinases in Xenopus laevis

Area of Science:

• Molecular Biology
• Biochemistry
• Genetics

Background:

• Nucleoside diphosphate kinases (NDPKs) are crucial enzymes catalyzing nucleoside diphosphate phosphorylation.
• Mammalian NDPK is a hexamer of acidic (A) and basic (B) subunits; prokaryotes and invertebrates have a single cytoplasmic form.
• Chloroplastic, mitochondrial, and related protein genes have also been identified.

Purpose of the Study:

• To investigate the gene structure and function of cytoplasmic NDPK in Xenopus laevis.
• To explore the potential autoregulatory mechanisms of NDPK in this species.
• To compare Xenopus NDPK genes with their human counterparts and analyze evolutionary diversification.

Main Methods:

• Gene cloning and sequence analysis of Xenopus laevis NDPK.
• In vitro binding assays of Xenopus X1 NDPK to DNA elements (human c-myc promoter NHE, CT dinucleotide repeat).
• Phylogenetic analysis of vertebrate NDPK sequences.

Main Results:

• Xenopus laevis possesses multiple homologous genes encoding cytoplasmic NDPK, with each monomer encoded by two genes due to pseudotetraploidy.
• Xenopus NDPK genes share high sequence identity (82-87%) with human orthologs.
• Xenopus X1 NDPK binds to the nuclease hypersensitive element (NHE) of the human c-myc promoter and CT dinucleotide repeats.
• The NHE sequence is found in the 3' non-coding region of Xenopus NDPK genes, suggesting potential mRNA binding.

Conclusions:

• Xenopus cytoplasmic NDPK, like its mammalian counterpart, is encoded by multiple genes, indicating functional diversification through gene duplication.
• NDPK may bind to its own mRNA's 3' non-coding region, potentially inhibiting polyadenylation and establishing an autoregulatory translation control.
• Phylogenetic analysis supports gene duplication as a driver of NDPK functional diversification in vertebrates, particularly in amphibians.