The growth, supercoiling and movement of the macrofiber shown in Fig. 8. Filled circles on the bottom curve (B) are measured lengths, open squares are theoretical projections of continued length extension based upon the initial growth rate. Open circles represent the calculated fiber length from the tether obtained by subtracting the length of fiber shaft shortened by its incorporation into plectoneme supercoils from the projected maximum length obtained by fiber growth. The upper curves (A) show the times at which supercoils formed and their distance from the tether. Points on the upper curve correspond to the same time axis as those on the lower curve. Points aligned beneath one another on the upper curve indicate the movement of a supercoil toward the tether. The first three supercoils arose close to the tether and therefore did not move. Later arising supercoils were prevented from moving all the way to the tether by the mass of fiber accumulated there from earlier supercoils as shown in additional file 4. (Two triangles connected with a horizontal line on panel B indicate the starting [336 minutes] and ending [472 minutes] times corresponding to the film sequence shown in additional file 4.) Preferred locations for supercoil initiation were initially at the tether, then at the surface of fiber mass attached to the tether. At later times supercoils arose at distances of approximately 1.5 and 2.6 mm from the tether. A total of 29 supercoils were observed.