EIA virus was purified from equine fetal kidney cell cultures by PEG-precipitation, two sucrose-gradient sedimentations (5-30 per cent) and (25 to 60 per cent) centrifugation, using the immunodiffusion test to follow the procedure. Purified EIA virus had a density (20 degrees C) of 1.162 and a sedimentation constant of S20w=656. electron microscopy revealed a particle of about 100 nm in diameter with a very flexible but usually spherical shape. The dense core may be at various locations inside the membrane bound particle.

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Morphological studies of EIAV reveal knobs on the surface of the particles, conically and tubularly shaped cores, budding particles with dense crescents directly underlying the plasma membrane, and distinct intracytoplasmic structures in infected cells.

Sequences of amino acids at the N-termini of virus proteins VP,, VP2, and VP. were determined for foot-and-mouth disease virus types A12 strain 119, 01 Brugge and C3 Resende. In the polyacrylamide gel electrophoresis system used to purify the proteins, VP, migrated faster than VP1 or VP2; and in the virion, VP. could be cleaved by trypsin into VP. and VPsb. The N-terminal amino acids for each of the virus types were glycine in VP,, aspartic acid in VP2, and threonine in VP,. No divergences in sequence across the virus types were indicated until at least the fourth position in VP1, the second in VP2, and the third in VP3. For virus types A12, 01 and C,, the sequences were, respectively: for VP1 (Gly-ile-phe,pro,val-), (Gly,ile,phe-) and (Gly-ile-phe,ala-); for VP2 (Asp,X,met-), (Asp-) and Asp-leu-); and for VP.3 (Thr-thr-ala-thr-), (Thr-thr-ser-) and (Thr-thr-). Unresolved mixtures of VP. and VPSb, from either type A12 or 01 viruses, appeared to have the N-terminal amino acids threonine, which is presumed to be the same threonine as in uncleaved VP3 and serine, which is generated by the tryptic cleavage. Foot-and-mouth disease virus (FMDV) is an acid-sensitive picornavirus that contains four capsid proteins, three of which comprise approximately 91% of the total protein. In a previous paper, Bachrach et al. (2) isolated each of the three major proteins of type A,2 virus by preparative polyacrylamide gel electrophoresis (PAGE) and determined their C-terminal sequences by the use of carboxypeptidase A. Recently, we examined the N-terminal amino acid residues of the three major proteins of type A,2 virus and found them to be similar to those reported for type 01 Kaufbeuren by Adam and Strohmaier (1). This paper reports our findings on the N-termini of the three major proteins of FMDV types A,2 strain 119, 01 Brugge and C2 Resende, as well as on short sequences of amino acids at the N-termini of these proteins. MATERIALS AND METHODS Virus and virus proteins. FMDV types A12 strain