Direct interaction between hnRNP-M and CDC5L/PLRG1 proteins affects alternative splice site choice

Heterogeneous nuclear ribonucleoprotein‐M (hnRNP‐M) is an abundant nuclear protein that binds to pre‐mRNA and is a component of the spliceosome complex. A direct interaction was detected in vivo between hnRNP‐M and the human spliceosome proteins cell division cycle 5‐like (CDC5L) and pleiotropic regulator 1 (PLRG1) that was inhibited during the heat‐shock stress response. A central region in hnRNP‐M is required for interaction with CDC5L/PLRG1. hnRNP‐M affects both 5′ and 3′ alternative splice site choices, and an hnRNP‐M mutant lacking the CDC5L/PLRG1 interaction domain is unable to modulate alternative splicing of an adeno‐E1A mini‐gene substrate. By combining proteomic and biochemical approaches with live cell imaging including FLIM‐FRET and FRAP, Lamond and colleagues provide evidence for a direct involvement of hnRNP M in the spliceosome machinery through its interaction with the hCDC5L/hPLRG1 subcomplex. These results provide new insight into the mechanism whereby hnRNP M can modulate both 5′ and 3′ splice site choice.