Modification of the Leader Protein (Lb) of Foot-and-Mouth Disease Virus

Translation of foot-and-mouth disease virus RNA for extended periods in rabbit reticulocyte lysates results in the appearance of a previously undescribed protein. A protein with similar properties can also be detected in BHK cells at late times after virus infection. Specific immunoprecipitation has shown that this protein (Lb') is closely related to the smaller of the two leader proteins, Lb, although it migrates with an apparently higher M_r in SDS-polyacrylamide gels. The conversion of Lb to Lb' can be mimicked by treatment with carboxypeptidase B. It is suggested that C-terminal trimming of Lb to produce Lb' results in an increase in negative charge and is responsible for its slower migration in SDS-PAGE.