Involved in protein export. Acts as a chaperone by maintaining the newly synthesized secretory and non-secretory proteins in an open conformation. Binds to 3 regions of unfolded substrate PhoA, preferring aromatic and hydrophobic residues, keeping it stretched out and unable to form aggregates (PubMed:24812405). Binds to nascent polypeptide chains via ribosomal protein L23 (PubMed:12226666). Functions as a peptidyl-prolyl cis-trans isomerase in vitro, this activity is dispensible in vivo for chaperone activity. [protein]-peptidylproline (omega=180) = [protein]-peptidylproline (omega=0) Homodimer and monomer. In vivo most of the ribosomes are in complex with monomeric TF (PubMed:12452438); binding as a dimer has also been suggested (PubMed:12581648). Uncomplexed TF is in a monomer-dimer equilibrium with approximately two thirds of TF existing in a dimeric state; binding to substrate PhoA induces monomerization, 3 TF monomers bind somewhat independently to a single substrate molecule (PubMed:12452438, PubMed:24812405). TF and SRP can simultaneously bind to ribosomes; TF binding is abolished when SRP is bound to FtsY in the presence of a non-hydrolyzable GTP analog (PubMed:15148364). Contacts ribosomal proteins L23 and L29 (PubMed:12226666). About half TF is bound to the ribosome near the polypeptide exit tunnel while the other half is free in the cytoplasm. Consists of 3 domains; the N-terminus (residues 1-112) binds the ribosome, the middle domain (residues 150-246) has PPIase activity, while the discontinuous C-terminus (residues 113-149 and 247-432) binds substrate and has intrinsic chaperone activity on its own. (Microbial infection) ADP-ribosylated by the phage T4 protein ModB. Non-essential; synthetic lethality is seen in a triple tig-dnaK-dnaJ disruption, although this depends on temperature (triple disruptions grow slowly at 20 and 34 degrees Celsius but not at all at 43 degrees) and strain background. Belongs to the FKBP-type PPIase family. Tig subfamily.