Die primäre Proteinstruktur von Stämmen des Tabakmosaikvirus

Summary

In contrast to chemically induced mutants of tobacco mosaic virus (TMV) in which we have found replacement of one or at most of two amino acids per coat protein chain, the protein chains of naturally occurring TMV strains differ from each other in numerous positions. The complete amino acid sequence of the naturally occurring TMV straindahlemense isolated byMelchers (1940) has been determined. It differs in 30 of the 158 amino acid positions from the TMV wild strainvulgare (Fig. 1). This is the first case in which complete amino acid sequences of the coat proteins of two virus strains can be compared. Such a comparison permits conclusions about the structure of the protein subunits and about certain aspects of the genetic code to be drawn.

The electrophoretic mobility curves for the virus rods and the A proteins ofvulgare anddahlemense (Fig. 4) can be explained on the basis of the amino acid sequences of the two strains. Spatial distribution of the positive and negative groups within the protein subunits are discussed. One particular segment of the protein chain appears to be so important for the secondary and/or tertiary structure of the protein subunit that amino acid replacements within this segment in general lead to a loss of infectivity.

The 46 cases in which we have exactly located the positions of amino acid differences betweenvulgare and various TMV mutants and strains are summarized in Table 1. Combination of the data in Table 1 with the base compositions of the triplets as obtained from the cell free system ofE. coli permits conclusions about the nucleotide sequence within the triplets to be drawn. The triplets shown in Table 2 represent, at present, the best agreement between the data from the cell free system and the work with TMV mutants.