Elongation factor specific for Sec in eukaryotes is
Eukaryotic selenocysteine delivery requires dedicated elongation factor eEFSec or EFSec, paralogous to canonical eEF1A but unable to bind standard aminoacyl-tRNAs. EFSec contains unique domain IV interacting with SBP2-SECIS complex and extended C-terminus specifically recognizing tRNASec distinct features including long variable arm and 13-base-pair acceptor-TΨC stack. GTP-bound EFSec delivers Sec-tRNASec to ribosomal A-site when UGA occupies decoding center, with GTP hydrolysis enabling accommodation and peptide transfer. This selectivity prevents misincorporation of biosynthetic intermediate
Ref: Alberts et al., Molecular Biology of the Cell, 7th ed., Chapter 6: EFSec – Sec-Specific Elongation Factor