Polypeptide chain initiation in eukaryotes: initiation factor MP in Artemia salina embryos.

The activity of IF-MP, a polypeptide chain initiation factor that forms a ternary complex with eukaryotic initiator Met-tRNA and GTP and promotes binding of the initiator to 40S ribosomes, is very low in undeveloped Artemia salina embryos but increases over 20-fold following resumption of development upon hydration of the cysts. The factor is present in both the ribosomal salt wash and high-speed-supernatant. Its specific activity is 50 times higher in the wash but its total activity is only about twice as high in the wash as in the supernatant. As is true of IF-MP from other eukaryotic sources, the A. salina factor is specific for eukaryotic Met-tRNAi and sensitive to SH-reagents, and its activity is GTP dependent.