Definition: In this task, you're given a paragraph from the research paper and your task is to generate a suitable title for the research paper based on the given paper. Under 100 words is a good title length.
Input: The spike (S) glycoprotein of coronavirus is responsible for receptor binding and membrane fusion. A number of variants with deletions and mutations in the S protein have been isolated from naturally and persistently infected animals and tissue cultures. Here, we report the emergence and isolation of two temperature sensitive (ts) mutants and a revertant in the process of cold-adaptation of coronavirus infectious bronchitis virus (IBV) to a monkey kidney cell line. The complete sequences of wild type (wt) virus, two ts mutants, and the revertant were compared and variations linked to phenotypes were mapped. A single amino acid reversion (L 294 -to-Q) in the S protein is sufficient to abrogate the ts phenotype. Interestingly, unlike wt virus, the revertant grows well at and below 32 jC, the permissive temperature, as it carries other mutations in multiple genes that might be associated with the cold-adaptation phenotype. If the two ts mutants were allowed to enter cells at 32 jC, the S protein was synthesized, core-glycosylated and at least partially modified at 40 jC. However, compared with wt virus and the revertant, no infectious particles of these ts mutants were assembled and released from the ts mutant-infected cells at 40 jC. Evidence presented demonstrated that the Q 294 -to-L 294 mutation, located at a highly conserved domain of the S1 subunit, might hamper processing of the S protein to a matured 180-kDa, endo-glycosidase H-resistant glycoprotein and the translocation of the protein to the cell surface. Consequently, some essential functions of the S protein, including mediation of cell-to-cell fusion and its incorporation into virions, were completely abolished. D

A single amino acid mutation in the spike protein of coronavirus infectious bronchitis virus hampers its maturation and incorporation into virions at the nonpermissive temperature