The beta-tubulin monomer release factor (p14) has homology with a region of the DnaJ protein.

p14 is a molecular chaperone involved in beta-tubulin folding which catalyzes the release of beta-tubulin monomers from intermediate complexes. Here we demonstrate that active p14 protein which we have purified from an overproducing Escherichia coli strain can also release beta-tubulin monomers from tubulin dimers in the presence of an additional cofactor (Z). Analysis of p14 secondary structure suggests that this protein may belong to a family of conserved proteins which share structural similarities with the J-domain of DnaJ. We have constructed deletions and site-directed mutations in the p14 gene. A single D to E mutation in the region shown in DnaJ to be an essential loop for its function affected the monomer-release activity of p14. These results support the hypothesis that this p14 loop interacts with beta-tubulin in a similar fashion as DnaJ interacts with DnaK and suggest a possible role of p14 in the folding process.