LINEAR BIOSYNTHESIS OF TOBACCO MOSAIC VIRUS: INCORPORATION OF C 14 INTO RODS OF DIFFERENT LENGTHS

Publisher Website
Google Scholar
Abstract
(1) The C14 content of tobacco mosaic virus (TMV) rods, following photosynthetic assimilation of C14O2 by infected tobacco leaf, has been determined as a function of rod length and time of C14 incorporation. In all cases, the specific activity of short rods is considerably higher than the specific activity of 3000 A rods isolated from the same original TMV preparation. When the duration of un-labeled CO2 incorporation is varied, following a 15-minute pulse of C14(32, the difference in specific activity between 3000 A rods and short rods is maintained. This is evidence that the short rods present in the TMV extract are not converted to 3000 A rods during the course of the experiment. The RNA content and the RNA nucleotide composition of short rods and 3000 A rods are not significantly different. Both the RNA fiber and the array of protein subunits are shortened proportionally in short rods. Differences between C14 specific activities of the protein of short rods and of 3000 A rods are accompanied by comparable differences between the specific activities of their respective RNA nucleotides. Analysis of the C14 content of successive linear segments of protein removed from a homogeneous preparation of 3000 A rods (by treatment with detergent) confirms earlier experiments with inhomogeneous TMV preparations. The observed variations in the C14 content of successive segments of the rods indicate that they are formed by a process of linear accretion of protein substance. There are systematic relationships among rod length, specific activity, and duration of C14 incorporation, which will permit an analysis of linear processes in TMV biosynthesis.