Structure, Transcription, and Replication of Measles Virus

Abstract

Measles virus, a member of the morbillivirus genus of the paramyxovirus family, is an enveloped virus containing a single-stranded, minus (−) sense 50S RNA genome (Baczko et al. 1983; Dunlap et al. 1983; Udem and Cook 1984). Negatively stained preparations of virus particles appear roughly spherical but pleomorphic by electron microscopy, with the diameters of the particles ranging from 300 um to 1000 um (Lund et al. 1984). The envelope of the virion consists of a lipid bilayer membrane; the integral viral membrane proteins hemagglutinin (H, 80 kDa) (Gerald et al. 1986) and the two subunits of the fusion protein (F1, 40 kDa and F2, 20 kDa) (Buckland et al. 1987; Richardson et al. 1986; Stallcup et al. 1979) can be released by trypsin treatment. The matrix protein (M, 37 kDa) (Greer et al. 1986) appears to lie on the inner surface of the membrane and can be released with detergent and high salt (Bellini et al. 1986; Stallcup et al. 1979). Virion RNA is packaged in a helical ribonucleoprotein particle or nucleocapsid (Nakai et al. 1969; Robbins et al. 1980; and Lund et al. 1984) by the nucleocapsid protein (N, 60 kDa) (Rozenblatt et al. 1985). Measles nucleocapsids can be purified from virus banded on CsCI gradients as ribonucleoprotein particles at a density of 1.32 g/cm³ (Stallcup et al. 1979; Robbins et al. 1980; Udem and Cook 1984). The association between RNA and N is very stable, being resistant to dissociation by high salt, and the encapsidated RNA is resistant to nuclease digestion (Andzhaparidze et al. 1987; Moyer et al. 1990). The virus-encoded RNA-dependent RNA polymerase consists of two subunits, the P (70 kDa) and L (~250 kDa) proteins, and is associated with the nucleocapsid in the virion (Bellini et al. 1985; Blumber et al. 1988; Seifried et al. 1978).