Potential function of THOC5 in immediate-early gene response. Upon stimulation with growth factors/cytokines THOC5 is phosphorylated at multiple positions. Signals reach the nucleus and the promoters of immediate-early response genes are activated. Simultaneously, the 3′ processing complex is recruited to the promoter region . During gene transcription, THOC5 is recruited to its target immediate-early gene  and then participates in 3′ processing of these genes. Unspliced and spliced THOC5 target mRNAs form a complex with THOC5. Post transcriptional splicing occurs in nuclear speckles where THOC5 has accumulated . For the export of spliced mRNAs from nuclear speckles other members of TREX, Aly, UAP56 and THOC2 are required [30, 44]. It has been suggested that THOC5 and Aly form a complex with mRNA receptor TAP-p15 transiently and transfer THOC5 target mRNA to the TAP-p15 complex . PM: plasma membrane; NP: nuclear pore.