Genes in the DNAJ family provide instructions for making proteins that play a role in various cellular functions, such as proper protein folding, protein transport, and the cell's response to stress. DNAJ proteins are active in cells and tissues throughout the body.

The main work of DNAJ proteins is protein folding. After proteins are produced, they must be folded into the correct 3-dimensional shape to function properly. Proteins that help with this 3-dimensional folding are called chaperones. The role of a chaperone is to bind to unfolded or partially folded proteins, prevent misfolding, and assemble or disassemble multi-protein structures. DNAJ proteins are known as co-chaperones because they help another family of chaperones (DNAKs) with protein folding. DNAJ and DNAK proteins must work together to facilitate protein folding.

Researchers have found three types of DNAJ proteins. All DNAJ family members have a region of 70 protein building blocks (amino acids) known as the J-domain, which is the site of interaction between DNAJ proteins and DNAK proteins. Type I DNAJ proteins are considered true DNAJ proteins, while types II and III are usually referred to as DNAJ-like proteins. Most of the genes in this family are designated by the letters DNAJ (J for the J-domain) and an additional letter indicating the subgroup to which they belong. The subgroup designation is based on the type of DNAJ protein (type I is A, type II is B, type III is C). They also receive a number to designate the specific gene within the subgroup, for example DNAJC19. DNAJ proteins are also known as Hsp40s (heat shock protein 40); DNAK proteins also are referred to as Hsp70s.mily provide instructions for making proteins that play a role in various cellular functions, such as proper protein folding, protein transport, and the cell's response to stress. DNAJ proteins are active in cells and tissues throughout the body.