Inner membrane protein required for the insertion and/or proper folding and/or complex formation of integral inner membrane proteins. Involved in integration of membrane proteins that insert dependently and independently of the Sec translocase complex, as well as at least 2 lipoproteins. Its own insertion requires SRP and is Sec translocase-dependent. Essential for the integration of Sec-dependent subunit a of the F(0)ATP synthase, FtsQ and SecE proteins and for Sec-independent subunit c of the F(0)ATP synthase, M13 phage procoat and the N-terminus of leader peptidase Lep. Probably interacts directly with Sec-independent substrates. Sec-dependent protein FtsQ interacts first with SecY then subsequently with YidC. Sec-dependent LacY and MalF require YidC to acquire tertiary structure and stability, a chaperone-like function, but not for membrane insertion. Stable maltose transport copmplex formation (MalFGK(2)) also requires YidC. Partially complements a Streptococcus mutans yidC2 disruption mutant. Interacts with SecD and SecF. Component of the SecDF-YajC complex, a heterotetrameric translocase complex. The SecDF-YidC-YajC translocase forms a supercomplex with SecYEG, called the holo-translocon (HTL) (PubMed:27435098). The stoichiometry of the super complex may be SecYEG:YidC:SecDF 4:3:1, YajC is in the reconstituted complex (with SecDF) but as no antibody is available it could not be quantified (PubMed:27435098). Specifically interacts with transmembrane segments of nascent integral membrane proteins during membrane integration. Found in 3 different complexes in inner membrane preparations (PubMed:16079137). Can be cross-linked to FtsH, in the larger FtsH/HflKC complex. Predominantly localized at cell poles at all stages of cell growth. At mid-exponential phase in strain MC4100 there are about 2500 copies per cell (at protein level). Most of the large periplasmic domain (residues 24-264) is not required for either Sec-dependent or Sec-independent protein insertion. However, residues 265-346, the C-terminal part of the large periplasmic domain, are required for both Sec-dependent and Sec-independent protein insertion. Lethality. Upon depletion experiments insertion of Sec translocase-independent integral membrane proteins ceases. Translocation of Sec-dependent protein decreases to a lesser extent. Also leads to decreased targeting and/or translocation of Lpp and BRP lipoproteins. Both spoIIIJ and yqjG of B.subtilis functionally complement yidC depletion, whereas Streptococcus mutans yidC1 and yidC2 only partially complement depletion. Belongs to the OXA1/ALB3/YidC family. Type 1 subfamily.