A NEW YEAST TRANSLATION INITIATION-FACTOR SUPPRESSES A MUTATION IN THE ELF-4A RNA HELICASE

We have isolated a gene, STM1, which encodes a new translation initiat ion factor from Saccharomyces cerevisiae. The gene acts, if present on a multicopy plasmid, as a suppressor of a temperature-sensitive mutat ion in eIF-4A. The single copy STM1 gene is not essential, but disrupt ion causes a slow growth phenotype. Analysis of polysomes from a strai n carrying a disrupted stm1 allele shows a clear defect in translation initiation as shown by a strong reduction in polysomes and an increas e in the monosomes. Sequence analysis revealed interesting features of the putative Stm1 protein. Comparison of the entire protein sequence with databanks showed some similarity with the human eIF-4B protein. T he Stm1 protein has potential RNP1 and RNP2 motifs characteristic for RNA-binding proteins. The protein also contains six highly conserved d irect repeats of 21-26 amino acids and one partial repeat.