What are other degradation pathways?

-Four additional degradation pathways involve regulated degradation of specific mRNAs. -Deadenylation-independent decapping proceeds in the presence of a long poly(A) tail. -The degradation of the nonpolyadenylated histone mRNAs is initiated by 3′ addition of a poly(U) tail. -Degradation of some mRNAs may be initiated by sequence-specific or structure-specific endonucleolytic cleavage. -An unknown number of mRNAs are targets for degradation or translational repression by microRNAs (miRNAs).