Occurrence of multiple ribonucleotide reductase classes in gamma-Proteobacteria species

Ribonucleotide reductase (RNR) is central to de novo synthesis of deoxyribo nucleotides and essential for all living cells. Three classes have been des cribed; class I is oxygen dependent and represented by two subclasses, Ia ( NrdAB) and Ib (NrdEF); class II (NrdJ) is indifferent to oxygen; and class III (NrdDG) is oxygen sensitive. More than one class can be found in an org anism, reflecting the oxygen status of its environment. We have investigate d, by using PCR and Southern blot, the occurrence of the different classes among species of the gamma -Proteobacteria. Class III an present in all spe cies tested, hut the presence of the other classes varies. Some species con tain one unique additional enzyme, class Ia, Ib, or II, whereas others cont ain two additional enzymes, class Ia and Ib, or class Ia and II.