Some Properties of a Temperature-sensitive Mutant of Cowpea Chlorotic Mottle Virus

Abstract

SUMMARY The behaviour and properties of a temperature-sensitive mutant of cowpea chlorotic mottle virus are described. The mutant multiplied well at 21° but, unlike the wild-type, only slightly at 32° although considerable amounts of uncoated RNA accumulated in inoculated leaves at this temperature. The specific infectivity of the mutant was much lower than that of the wild-type virus because the largest species of encapsidated mutant RNA was almost completely degraded even in virus from plants grown at 21°. The temperature sensitivity and low specific infectivity of the mutant were related to properties of its coat protein, which was much less heat stable than that of the wild-type virus. Glutamic acid and alanine replaced lysine and valine respectively in the mutant coat protein and these replacements, in addition to affecting thermal stability, influenced the polymerization of isolated protein at pH 6.7.