text: A number of bacterial mRNAs have no 5'UTR whatsoever, or a very short one. The complete 70S ribosome, with the help of IF2 (recruiting fMet-tRNA), can simply start translating such a "leaderless" mRNA.
  A number of factors modify the efficiency of leaderless initiation. A 5 phosphate group attached to the start codon seems near-essential. AUG is strongly preferred in E. coli, but not necessarily in other species. IF3 inhibits leaderless initiation. A longer 5UTR or one with significant secondary structure also inhibits leaderless initiation.