Further identification and characterization of novel intermediate and mature cleavage products released from the ORF 1b region of the avian coronavirus infectious bronchitis virus 1a/1b polyprotein

The coronavirus 3C-like proteinase is one of the viral proteinases responsi ble for processing of the 1a and 1a/1b polyproteins to multiple mature prod ucts. In cells infected with avian coronavirus infectious bronchitis virus (IBV), three proteins of 100, 39, and 35 kDa, respectively were previously identified as mature cleavage products released from the 1b region of the 1 a/1b polyprotein by the 3C-like proteinase. In this report, we show the ide ntification of two more cleavage products of 68 and 58 kDa released from th e same region of the polyprotein. In addition, two stable intermediate clea vage products with molecular masses of 160 and 132 kDa, respectively, were identified in IBV-infected cells. The 160-kDa protein was shown to be an in termediate cleavage product covering the 100- and 68-kDa proteins, and the 132-kDa protein to be an intermediate cleavage product covering the 58-, 39 -, and 35-kDa proteins. Immunofluorescent staining of IBV-infected cells an d cells expressing, individual cleavage products showed that the 100-, 68-, and 58-kDa proteins were associated with the membranes of the endoplasmic reticulum, and the 39- and 35-kDa proteins displayed diffuse distribution p atterns. (C) 2001 Academic Press.