LINEAR BIOSYNTHESIS OF TOBACCO MOSAIC VIRUS: CHANGES IN ROD LENGTH DURING THE COURSE OF INFECTION

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Abstract
Rods 3,000 A [plus or minus] 300 A long (M) and shorter rods (S) are natural products of tobacco mosaic virus (TMV) replication. S rods predominate in TMV isolated one day after inoculation; the proportion of S rods falls to a constant value of 50% at 3-5 days after inoculation. S rods appear to be unifectious but are identical to M rods in RNA:protein ratio and in serological specificity. The apparent rate constant of TMV production, based on the synthesis of M and S rods at sites established by M rods only, falls linearly during the first few days after inoculation; this suggests the effect of radial enlargement of the zone infection during that period. The relatively low concentration of S rods during the early stages of the infection remains unexplained but may be due to the preferential binding of M rods to an insoluble component of newly infected tissue. These observations are consistent with, but do not prove, an hypothesis of TMV biosynthesis by a process of linear growth. In this case, the S rods, which are commonly observed in TMV preparations, would represent aborted rods; short rods actually in process of growth appear to be unextractable by the methods used to isolate ordinary TMV.