Mr. Abid et al., Translational regulation of ribonucleotide reductase by eukaryotic initiation factor 4E links protein synthesis to the control of DNA replication, J BIOL CHEM, 274(50), 1999, pp. 35991-35998
Ribonucleotide reductase synthesizes dNDPs, a specific and limiting step in
DNA synthesis, and can participate in neoplastic transformation when overe
xpressed, The small subunit (ribonucleotide reductase 2 (RNR2)) was cloned
as a major product in a subtraction library from eukaryotic initiation fact
or 4E (eIF4E)-transformed cells (Chinese hamster ovary-4E (CHO-4E)), CHO-4E
cells have 20-40-fold elevated RNR2 protein, reflecting an increased distr
ibution of RNR2 mRNA to the heavy polysomes, CHO-4E cells display an altere
d cell cycle with shortened S phase, similar to cells selected for RNR2 ove
rexpression with hydroxyurea, The function of ribonucleotide reductase as a
checkpoint component of S progression was studied in yeast in which elevat
ed eIF4E rescued S-arrested rnr2-68(ts) cells, by increasing recruitment of
its mRNA to polysomes, Crosses between rnr2-68(ts) and mutant eIF4E (cdc33
-1(ts)) engendered conditional synthetic lethality, with extreme sensitivit
y to hydroxyurea and the microtubule depolymerizing agent, benomyl. The dou
ble mutant (cdc33-1 rnr2-68) also identified a unique terminal phenotype, a
rrested with small bud and a randomly distributed single nucleus, which is
distinct from those of both parental single mutants. This phenotype defines
eIF4E and RNR2 as determinants in an important cell cycle checkpoint, in e
arly/mid-S phase. These results also provide a link between protein and DNA
synthesis and provide an explanation for cell cycle alterations induced by
elevated eIF4E.