 In shunting, after the 40S ribosome starts sliding along the mRNA it "jumps" or skips large sections; the mechanism for this is still unclear.eIF4G is required for most types of initiation, except in special cases such as internal initiation at the HCV IRES or Cripavirus IRES.eIF4G is an initiation factor involved in the assembly of the 43S and 48S 43S_preinitiation_complex.