The formation of a large multiprotein-DNA complex that self-assembles on gene promoter through the sequential recruitment of the general initiation factors that compose the preinitiation complex (PIC) (which includes including UBF, SL1, RRN3 and TBP in human). The PIC engages RNA polymerase I on its DNA template strand and sparks polymerization of the first few RNA nucleotides.
RNA polymerase I transcriptional preinitiation complex assembly