Kinetics of Synthesis of Respiratory Syncytial Virus Glycoproteins

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Abstract
The synthesis of the two respiratory syncytial (RS) virus glycoproteins (VP66 and VP84) was examined under standard conditions and after treatment with tunicamycin and monensin. The protein backbone for VP66, the fusion protein (F1.2) is co-translationally glycosylated to form F0, which is cleaved to form F1.2 by 20 min of chase. Monensin treatment inhibited the cleavage of FO over an 80 min chase period, indicating that this occurred late in the transit of FO through the Golgi apparatus or after exit from the Golgi apparatus. Tunicamycin treatment resulted in the synthesis of a 50K to 55K unglycosylated FO which is cleaved to a 40K protein. VP84, the large glycoprotein, contains a protein backbone of only 26K to 30K which is modified by N-linked and probable O-linked glycosylation. Tunicamycin treatment results in the synthesis of a 70K protein (p70) which incorporates [3H]glucosamine and [3H]fucose but not [3H]mannose. Glycosylated precursors varying in mol. wt. from 29K to 45K (p45) are found in infected cells at regular 2K to 3K intervals, producing a ''ladder'' effect. The step from p45 to VP84 is severely delayed by monensin treatment thereby enhancing the ''ladder'' effect of the precursors.