Obstacles to Scanning by RNase E Govern Bacterial mRNA Lifetimes by Hindering Access to Distal Cleavage Sites

？ A monophosphorylated 5′ end stimulates mRNA degradation by the endonuclease RNase E ？ Its ability to cut is hindered by obstacles between the 5′ end and cleavage sites ？ Effective obstacles include bound ribosomes, proteins, and sRNAs ？ RNase E appears to scan RNA linearly from the 5′ end along single-stranded region