THE INTERFERON-INDUCED MX-PROTEIN OF CHICKENS LACKS ANTIVIRAL ACTIVITY

cDNA sequencing revealed that chick Mr protein consists of 705 amino a cids, Its 84 N-terminal amino acids show no significant sequence homol ogy to other Mr proteins, They are followed by 514 residues that inclu de a tripartite GTP binding consensus moth, This region shows 50-70% s equence identity to mammalian and duck Mr proteins, Sequences near the C terminus, including a leucine zipper motif, are also conserved, whe reas the intervening 19 amino acids lack sequence similarity, This uni que sequence corresponds to a highly variable region in mammalian Mr p roteins, suggesting that it serves as a spacer between functional doma ins, Chick and mouse cells transiently transfected with cDNA expressio n constructs synthesized chick Mr protein at a level that could easily be detected with specific antibodies, Chick Mr protein in such cells was mainly cytoplasmic and had a granular appearance, Permanently tran sfected cell lines expressing high levels of chick Mr protein could no t be established, suggesting low metabolic stability of chick Mr prote in or incompatibility with cell proliferation, The antiviral activity of chick Mr protein was tested at the single-cell level using immunofl uorescence techniques, Transfected cells expressing chick Mr protein s howed no enhanced resistance to influenza A virus, vesicular stomatiti s virus, Thogoto virus, or Sendai virus, Thus, chick Mr joins the list of Mr proteins without recognized antiviral activity, supporting the concept that Mr proteins serve unrelated functions.