A temperature-sensitive mutant of TMV with unstable coat protein

Abstract

A temperature-sensitive mutant of TMV with a functional defect in the coat protein was isolated after nitrous acid treatment of the common strain. At 23 ° infected plants contained characteristic nucleoprotein virions and crystalline inclusions composed of disks of viral coat protein. At 35 ° no such particles or inclusions were produced; only free viral RNA and insoluble viral protein were found. The coat protein isolated from the virus differed from common strain protein in that it was stable only in low ionic strength buffers at neutral pH, did not aggregate very readily into virus-like rods, and denatured readily when aggregated at low pH. The protein has two amino acid exchanges involving a change from threonine to alanine at position 81 and serine to phenylalanine at position 143.