Prevents both degradation and modification of T7 DNA by the host restriction-modification complex (PubMed:32039758, PubMed:1095770). Structural mimic of the phosphate backbone of B-form DNA that binds to and completely occupies the DNA-binding sites of all known families of the complex type I DNA restriction enzymes (PubMed:12235377, PubMed:32483229). Thereby, inhibits the restriction endonuclease activity and protects the phage genome as it penetrates into host cytoplasm (PubMed:12235377, PubMed:32483229). Inhibits host transcription by binding to the bacterial RNAP and competing with sigma factors (PubMed:32039758). Inhibits the host exclusion defense system BREX (PubMed:32338761). Homodimer (PubMed:32039758, PubMed:6257722). Interacts with HsdM (AC P08957), the M subunit of host type I methyltransferase restriction enzyme M.EcoKI; 1 Ocr dimer binds to M.EcoKI (PubMed:12235377, PubMed:19074193). Interacts with HsdR (AC P08956), the R subunit of host type I bifunctional endonuclease and methyltransferase restriction enzyme R.EcoKI; 2 Ocr dimers binds to R.EcoKI (PubMed:12235377, PubMed:32483229). Interacts with host PglX/BrxX (AC P0DUF9); this interaction decreases by 20% the pglX-mediated methylated sites required for self versus non-self differentiation by the host (PubMed:32338761).