Function
The completed 8-subunit complex binds to mRNA and "scans" from a 5' to 3' direction until it locates an initiation codon, at which point the Met-tRNAi(Met) binds to it.
Interactions
The complex assembles around the 5' end of mRNA, and then proceeds to scan along the molecule in the 3' direction. Upon identifying the Kozak sequence, which has the start codon (AUG) embedded within it, the pre-initiation complex binds and begins to recruit the other protein factors necessary for translation.
The assembly and operation of Human PIC occurs entirely in the cytosol.
Origin
3j8c originates in Homo sapiens, but similar proteins are found in virtually all eukaryotes.
Prokaryotes do not have a corresponding initiation complex - instead, most have some deviation of the Shine-Dalgarno sequence in the 5' untranslated region that the 30s ribosomal subunit binds to in order to initiate translation.
References
http://oca.weizmann.ac.il/oca-docs/fgij/fg.htm?mol=3J8C
http://www.proteopedia.org/wiki/index.php/3j8c
http://www.rcsb.org/pdb/explore.do?structureId=3j8c
