Separation and infectivity of circular and linear forms of potato spindle tuber viroid.

Abstract
Potato spindle tuber viroid can be separated into 2 fractions by polyacrylamide gel electrophoresis in the presence of formamide and urea. One fraction contains predominantly circular molecules; the 2nd fraction contains almost exclusively linear molecules. The purity of the fractions was estimated by EM of formaldehyde-denatured molecules. The length distributions of denatured circular and linear molecules were determined. Both circular and linear molecules were infectious [towards tomato.].