Replication of Western Equine Encephalomyelitis Virus II. Cytoplasmic Structure Involved in the Synthesis and Development of the Virions

Abstract

Analysis of the cytoplasmic fraction of chick embryo cells during the exponential phase of Western equine encephalomyelitis (WEE) virus growth showed that the viral ribonucleic acid (RNA) labeled by a short pulse with 3 H-uridine was associated with a structure which sedimented in sucrose density gradients with a coefficient of 65 S . The RNA extracted from this structure sedimented in sucrose density gradients at 26 S . After a longer period of exposure to 3 H-uridine, the radio-active viral RNA was associated with a structure which sedimented in sucrose density gradients as would materials with coefficients of about 140 S . The 140 S structure contained viral RNA and viral protein. It was shown that the 140 S structures are not virus-induced polysomes. The 140 S structure contained predominantly the 40 S type of viral RNA and some 26 S type. Electrophoretic analysis of the disrupted virion revealed that at least two proteins (types I and II) were present in the purified virion. Only type II protein was present in the 140 S structure. Unlike the virion, the 140 S structure did not contain any lipid which could be detected by the incorporation of 14 C-choline. These data suggest that the 140 S structure represents the internal nucleoprotein part of the virion. The rate of appearance of labeled virus lags behind that of the formation of the 140 S structure in infected cells. Pulse-chase experiments with 3 H-leucine suggest that the 140 S structure may represent a precursor to the virus particle. The results are discussed in terms of the maturation of WEE virus in the infected cells.