A rare combination of ribonucleotide reductases in the social amoeba Dictyostelium discoideum.
Ribonucleotide reductases (RNRs) catalyze the only pathway for de novo synthesis of deoxyribonucleotides needed for DNA replication and repair. The vast majority of eukaryotes encodes only a class I RNR, but interestingly some eukaryotes, including the social amoeba Dictyostelium discoideum, encode both a class I and a class II RNR. The amino acid sequence of the D. discoideum class I RNR is similar to other eukaryotic RNRs, whereas that of its class II RNR is most similar to the monomeric class II RNRs found in Lactobacillus spp. and a few other bacteria. Here we report the first study of RNRs in a eukaryotic organism that encodes class I and class II RNRs. Both classes of RNR genes were expressed in D. discoideum cells, although the class I transcripts were more abundant and strongly enriched during mid-development compared with the class II transcript. The quaternary structure, allosteric regulation, and properties of the diiron-oxo/radical cofactor of D. discoideum class I RNR are similar to those of the mammalian RNRs. Inhibition of D. discoideum class I RNR by hydroxyurea resulted in a 90% reduction in spore formation and decreased the germination viability of the surviving spores by 75%. Class II RNR could not compensate for class I inhibition during development, and an excess of vitamin B12 coenzyme, which is essential for class II activity, did not improve spore formation. We suggest that class I is the principal RNR during D. discoideum development and growth and is important for spore formation, possibly by providing dNTPs for mitochondrial replication.
Department of Molecular Biology and Functional Genomics, Arrhenius Laboratories for Natural Sciences, Stockholm University, SE-10691 Stockholm, Sweden.
Mikael
M
Crona
Department of Molecular Biology, Swedish University of Agricultural Sciences, Uppsala Biomedical Center, SE-75124 Uppsala, Sweden.
Lotta
L
Avesson
Department of Molecular Biology and Functional Genomics, Arrhenius Laboratories for Natural Sciences, Stockholm University, SE-10691 Stockholm, Sweden; Department of Biochemistry and Biophysics, Stockholm University, SE-10691 Stockholm, Sweden.
Margareta
M
Sahlin
Department of Biochemistry and Biophysics, Stockholm University, SE-10691 Stockholm, Sweden.
Daniel
D
Lundin
Department of Molecular Biology, Swedish University of Agricultural Sciences, Uppsala Biomedical Center, SE-75124 Uppsala, Sweden.
Andrea
A
Hinas
Department of Molecular Biology and Functional Genomics, Arrhenius Laboratories for Natural Sciences, Stockholm University, SE-10691 Stockholm, Sweden.
Ralph
R
Klose
Department of Molecular Biology, Swedish University of Agricultural Sciences, Uppsala Biomedical Center, SE-75124 Uppsala, Sweden.
Fredrik
F
Söderbom
Department of Molecular Biology and Functional Genomics, Arrhenius Laboratories for Natural Sciences, Stockholm University, SE-10691 Stockholm, Sweden; Department of Biochemistry and Biophysics, Stockholm University, SE-10691 Stockholm, Sweden. Electronic address: britt-marie.sjoberg@dbb.su.se.
Britt-Marie
BM
Sjöberg
D000494:Allosteric Regulation; D056831:Coordination Complexes / Q000737:chemistry; D003565:Cytidine Diphosphate / Q000737:chemistry; D004023:Dictyostelium / Q000201:enzymology* / Q000235:genetics / Q000502:physiology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005609:Free Radicals / Q000737:chemistry; D015870:Gene Expression; D015971:Gene Expression Regulation, Enzymologic; D006153:Guanosine Diphosphate / Q000737:chemistry; D007501:Iron / Q000737:chemistry; D007700:Kinetics; D010802:Phylogeny; D015800:Protozoan Proteins / Q000235:genetics / Q000378:metabolism*; D012264:Ribonucleotide Reductases / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D013056:Spectrophotometry, Ultraviolet; D033761:Spores, Protozoan / Q000201:enzymology / Q000235:genetics; D014443:Tyrosine / Q000737:chemistry
D056831:Coordination Complexes; D004791:Enzyme Inhibitors; D005609:Free Radicals; D015800:Protozoan Proteins; D006153:Guanosine Diphosphate; D014443:Tyrosine; D003565:Cytidine Diphosphate; D007501:Iron; D012264:Ribonucleotide Reductases