Identification and RNA-binding properties of an initiation factor capable of relieving translational inhibition induced by heme deprivation or double-stranded RNA

An initiation factor from rabbit reticulocytes can overcome the block in initiation of protein synthesis occurring in reticulocyte lysates when exogenous hemin is not present, or when double-stranded RNA is added. This factor has been identified with IF-MP, an initiation factor capable of forming ternary complexes with GTP and methionyl-tRNA_F. Initiation factor IF-M3 by itself is unable to overcome the block in initiation, but appears to stimulate this activity of IF-MP. IF-MP binds to single-stranded R17 RNA as well as to double-stranded RNA, while IF-M3 only binds to double-stranded RNA. The protein synthetic activity of IF-MP is sensitive to N-ethylmaleimide, but its ability to bind RNA is resistant.