Structural visualization of bacteriophage P22 portal protein. This computer model was visualized with UCSF ChimeraX software. Secondary structures are colour-coded: for alpha helices, yellow for B-sheets and green for loops. Portal proteins perform multiple roles involved in entry and exit of DNA (deoxyribonucleic acid) from the virus capsid. Bacteriophages, or phages, are viruses that infect bacteria. P22 phage infects Salmonella typhimurium virus and is used in genetic engineering research.