GCD14p, a repressor of GCN4 translation, cooperates with Gcd10p and Lhp1p in the maturation of initiator methionyl-tRNA in Saccharomyces cerevisiae

Gcd10p and Gcd14p were first identified genetically as repressors of GCN4 m RNA translation in Saccharomyces cerevisiae. Recent findings indicate that Gcd10p and Gcd14p reside in a nuclear complex required for the presence of 1-methyladenosine in tRNAs, Here we show that Gcd14p is an essential protei n with predicted binding motifs for S-adenosylmethionine, consistent with a direct function in tRNA methylation. Two different gcd14 mutants exhibit d efects in cell growth and accumulate high levels of initiator methionyl-tRN A (tRNA(i)(Met)) precursors containing 5' and 3' extensions, suggesting a d efect in processing of the primary transcript. Dosage suppressors of grd10 mutations, encoding tRN(i)(Met) (hcIMT1 to hcIMT4; he indicates that the ge ne is carried on a high-copy-number plasmid) or a homologue of human La pro tein implicated in tRNA 3'-end formation (hcLHP1), also suppressed gcd14 mu tations. In fact, the lethality of a GCD14 deletion was suppressed by hcIMT 4, indicating that the essential function of Gcd14p is required for biogene sis of tRNA(i)(Met). A mutation in GCD10 or deletion of LHP1 exacerbated th e defects in cell growth and expression of mature tRNA(i)(Met) in gcd14 mut ants, consistent with functional interactions between Gcd14p, Gcd10p, and L hp1p in vivo. Surprisingly, the amounts of NME1 and RPR1, the RNA component s of RNases P and MRP, were substantially lower in gcd14 lhp1::LEU2 double mutants than in the corresponding single mutants, whereas 5S rRNA was prese nt at wild-type levels. Our findings suggest that Gcd14p and Lhp1p cooperat e in the maturation of a subset of RNA polymerase III transcripts.