On the possible presence of a beta 2-microglobulin-like protein in extracts of livers from normal chickens and chickens with erythroblastosis--I. Recognition of a small-molecular weight (mol. wt 11,000) protein.

1. An extract from the livers of both normal chickens (N) and chickens infected with avian erythroblastosis virus (Eb) contains a small molecular weight protein (SMWP, mol. wt 11,000). 2. Double immunodiffusion studies with rabbit antiserum against fowl serum proteins shows a precipitin arc for SMWP in N and Eb extracts, which is continuous with one from one of the normal chicken serum proteins. 3. When treated with 60% saturated ammonium sulphate the SMWP in the liver extracts divides between the precipitate and the supernatant although the specific serological activity of Eb extracts (gag--or COFAL--determined antigenic activity) is restricted to the precipitated SMWP fraction. 4. The COFAL activity of Eb liver extracts could be associated with SMWP by its attachment to this protein, or this phenomenon of "association" could represent the result of changes in synthesis of SMWP or post-synthetic changes.