Fig. 4.

Multiple functions of TTP proteins in mRNA life. TTP and TIS11b have been shown to modulate 3′-end mRNA maturation and poly(A) site selection in the cell nucleus. Recruitment of TTP proteins onto ARE-containing transcripts may occur under some circumstances in the nucleus and interactions with the nuclear pore complex may modulate mRNA delivery to the cytoplasm. After destabilization of the circularized mRNA, recruitment of deadenylases may direct AU-rich mRNAs to either 5′- or 3′-decay. TIS11 proteins are component of Processing Bodies (PB, in yellow) as well as Stress Granules (SG, in blue) induced in stress conditions. They are involved in PBs nucleation and promote 5′-mediated decay of target transcripts as well as their sorting and escorting between PBs and SG (interaction with transportin). TTP also regulates AU-rich mediated translation as it has been shown to exclude ARE-containing RNAs from heavy polysomes. Specific protein interactions with TTP seem to increase (Cul4B) or decrease (Rck/p54) polysome loading of ARE-containing transcripts. See text for detailed description of these and other functions of TTP/TIS11 proteins