Cofactor involved in the regulation of various cellular mechanisms such as actin regulation, autophagy, chromatin regulation and DNA repair. In physiological conditions, interacts with cofactor JMY in the cytoplasm which prevents JMY's actin nucleation activity and ability to activate the Arp2/3 complex. Acts as a negative regulator of nutrient stress-induced autophagy by inhibiting JMY's interaction with MAP1LC3B, thereby preventing autophagosome formation (By similarity). Involves in tubulin autoregulation by promoting its degradation in response to excess soluble tubulin. To do so, associates with the active ribosome near the ribosome exit tunnel and with nascent tubulin polypeptides early during their translation, triggering tubulin mRNA-targeted degradation (By similarity). Following DNA damage, phosphorylated by DNA damage responsive protein kinases ATM and CHEK2, leading to its nuclear accumulation and stability. Nuclear TTC5/STRAP promotes the assembly of a stress-responsive p53/TP53 coactivator complex, which includes the coactivators JMY and p300, thereby increasing p53/TP53-dependent transcription and apoptosis. Also recruits arginine methyltransferase PRMT5 to p53/TP53 when DNA is damaged, allowing PRMT5 to methylate p53/TP53. In DNA stress conditions, also prevents p53/TP53 degradation by E3 ubiquitin ligase MDM2. Upon heat-shock stress, forms a chromatin-associated complex with heat-shock factor 1 HSF1 and p300/EP300 to stimulate heat-shock-responsive transcription, thereby increasing cell survival. Mitochondrial TTC5/STRAP interacts with ATP synthase subunit beta ATP5F1B which decreased ATP synthase activity and lowers mitochondrial ATP production, thereby regulating cellular respiration and mitochondrial-dependent apoptosis. Mitochondrial TTC5/STRAP also regulates p53/TP53-mediated apoptosis (By similarity). Interacts with JMY and p300/EP300; the interaction occurs in the nucleus and augments the association between JMY and p300/EP300 in response to DNA damage. Interacts with PRMT5; the interaction is DNA damage-dependent and promotes PRMT5 interaction with p53/TP53 and subsequent methylation. Forms a complex with HSF1 and p300/EP300; these interactions augment chromatin-bound HSF1 and p300/EP300 histone acetyltransferase activity, resulting in enhanced heat-shock-responsive transcription. Interacts with JMY; the interaction occurs in the cytoplasm and results in the inhibition of JYM's nucleation activity (By similarity). Interacts with ribosome-coding tubulin (via 60S subunit 28S rRNA and protein uL24/RPL26) and the N-terminal of nascent tubulin polypeptide (via alpha-tubulin MREC motif and beta-tubulin MREI motif); these interactions result in tubulin mRNA-targeted degradation (By similarity). Interacts with ATP5F1B; the interaction occurs in the mitochondria and results in ATP production decrease. Interacts with p53/TP53; the interaction occurs in the mitochondria and results in increased apoptosis (By similarity). Phosphorylation at Ser-203 results in nuclear localization, while unphosphorylated protein localizes to the cytoplasm. Nuclear localization may be necessary for DNA damage-dependent stabilization of the protein. The tetratricopep-repeat (TPR) motifs may function as protein interaction domains. Phosphorylation by ATM kinase induces nuclear accumulation while interfering with nuclear export, and phosphorylation by CHEK2 kinase enhances nuclear stability.