Downloaded from www.microbiologyresearch.org by IP: 54.227.92.206 On: Tue, 19 Jul 2016 02:22:41 J. gen. Virol. (1981), 55, 155-164. Printed in Great Britain Key words: 1B V polypeptides/IB V strains/glycoproteins/phosphoproteins 155 Polypeptides of Infectious Bronchitis Virus. I. Polypeptides of the Virion By B. LOMNICZI*t AND J. MORSER Department of Biological Sciences, University of Warwick, Coventry CV4 7AL, U.K. (Accepted 10 February 1981) SUMMARY Infectious bronchitis virus (IBV), strain Beaudette, grown in cultured cells con- tained five structural proteins with apparent mol. wt. of 170000 (p170), 94000 (gp94), 50000 (pp50) 30000 (gp30) and 26000 (p26). Both gp94 and gp30 are glycopeptides since they were labelled with [3H]glucosamine. The only phosphoryl- ated polypeptide was pp50, and both it and gp94 were occasionally resolved into two bands. Two other polypeptides with mol. wt. of 28 000 (p28) and 14 000 (p 14) were sometimes associated with the virus. In egg-grown virus two additional proteins were found with mol. wt. of 110000 (p110) and 75 000 (gp75). The cell protein, actin, was also found in highly purified IBV virions. Different serotypes of either tissue culture-grown or egg-grown virus showed one of the two distinct polypeptide patterns of IBV described by Nagy & Lomniczi (1979) and Collins & Alexander (1980a, b). Strain Beaudette gave a pattern characteristic of the M type, while strain Connecticut gave a pattern characteristic of the C type. The polypeptides present in Connecticut virus were p170, gp98, pp50, gp28 and p26. Thus, the differences between the two patterns involve the mobility of both the large (gp94/gp98) and small (gp30/gp28) glycopeptides. INTRODUCTION Coronaviruses form a distinct family of enveloped viruses with large single-stranded RNA genomes of positive polarity (for review, see Robb & Bond, 1979). In the last few years the molecular biology of coronaviruses has been extensively studied, and from studies on the protein structure of porcine (Garwes & Pocock, 1975; Pocock & Garwes, 1977), murine (Sturman, 1977, Sturman & Holmes, 1977; Wege et al., 1979; Bond et aL, 1979) and human coronaviruses (Hierholzer, 1976; Macnaughton, 1980) a consistent pattern for coronavirus proteinS has begun to emerge. There is an unglycosylated nucleoprotein (mol. wt. 50000 to 60000) in the inner part of the virion, one or two smaller polypeptides (mol. wt. 20000 to 30000) in the envelope and two or three large (mol. wt. 60000 to 120000) polypeptides, most of which are glycosylated, plus an even larger glycoprotein (mol. wt. 160000 to 200000) associated with the spikes. In the case of the avian coronavirus, infectious bronchitis virus (IBV), the prototype of the family, the picture is less clear (Bingham, 1975; Alexander & Collins, 1977; Macnaughton & Madge, 1977; Macnaughton et al., 1977). In these studies no very large tool. wt. > 150000 or small mol. wt. < 30000 major proteins were reported and a small glycoprotein, equivalent to the one in mammalian coronaviruses, was not found. Furthermore, no notable differences were observed when various strains were compared (Macnaughton & Madge, 1977). Recently, however, the protein pattern of 12 IBV strains belonging to seven known serotypes were compared and two distinct polypeptide patterns were recognized (Nagy & tPresent address: Veterinary Medical Research Institute of the Hungarian Academy of Sciences, 1581- Budapest, P.O. Box 18, Hungary. 0022-1317/81/0000-4496 $02.00 © 1981 SGM