DIHYDROFOLATE-REDUCTASE PROTEIN INHIBITS ITS OWN TRANSLATION BY BINDING TO DIHYDROFOLATE-REDUCTASE MESSENGER-RNA SEQUENCES WITHIN THE CODING REGION

Previous studies suggest that dihydrofolate reductase (DHFR) regulates its own translation. Moreover, intracellular levels of DHFR protein i ncrease following exposure to the antifolate methotrexate (MTX), sugge sting that MTX may release the translational inhibition mediated by DH FR [Chu et al. (1993) Biochemistry 32, 4756-4760; Ercikan et al. (1993 ) Adv. Exp. Med. Biol. 338, 537-540]. To further investigate the role of DHFR in translational autoregulation, we have considered the possib ility that DHFR directly contacts its cognate mRNA. Binding studies us ing a series of truncated DHFR mRNAs as probes localized the DHFR/RNA interaction to a 100-base-pair region containing two putative stem-loo p structures; initial studies indicated that both of these loop struct ures are involved in protein binding. Moreover, the binding of MTX to DHFR prevents interaction of the protein with its cognate mRNA, thereb y relieving translational autoregulation.