Importance of a 5 ' stem-loop for longevity of papA mRNA in Escherichia coli

High-level expression of the major pilus subunit (PapA) of uropathogenic st rains of Escherichia coli results in part from the unusually long lifetime of the mRNA that encodes this protein. Here we report that the longevity of papA mRNA derives in large measure from the protection afforded by its 5' untranslated region. This papA RNA segment can prolong the lifetime of an o therwise short-lived mRNA to which it is fused. In vivo alkylation studies indicate that, in its natural milieu, the papA message begins with a stem-l oop structure. This stem-loop is important for the stabilizing effect of th e papA 5' untranslated region, as evidenced by the significant acceleration in papA mRNA decay that results from its removal.