Translation termination is the final step that completes
the synthesis of a polypeptide. Premature translation
termination by introduction of a nonsense mutation leads
to the synthesis of a truncated protein. We report the
identification and characterization of the product of the
MTT1 gene, a helicase belonging to the Upf1-like
family of helicases that is involved in modulating translation
termination. MTT1 is homologous to UPF1,
a factor previously shown to function in both mRNA turnover
and translation termination. Overexpression of MTT1
induced a nonsense suppression phenotype in a wild-type
yeast strain. Nonsense suppression is apparently not due
to induction of [PSI+], even
though cooverexpression of HSP104 alleviated the
nonsense suppression phenotype observed in cells overexpressing
MTT1, suggesting a more direct role of Hsp104p
in the translation termination process. The MTT1
gene product was shown to interact with translation termination
factors and is localized to polysomes. Taken together,
these results indicate that at least two members of a family
of RNA helicases modulate translation termination efficiency
in cells.