Evidence in support of this hypothesis includes: (i) that the chicken adenovirus protein Gam-1 inactivates the SUMO conjugation pathway by targeting the SUMO E1 activating enzyme complex in order to stimulate viral transcription [63]; (ii) that a pathogenic bacterium impairs the SUMO modification pathway to enhance infection [64]; and (iii) that SUMO modification of transcriptional regulatory proteins is frequently associated with transcriptional repression [53]. Here, PROS1 is linked to infection.