Filament loop diameter

Figure 27-5 (A, B) Two possible models of the 30-nm chromatin fiber.55 (A) Thoma et al.85 (B) Woodcock et al.6i 87 The fully compacted structure is seen at the top of each figure. The bottom parts of the figures illustrate proposed intermediate steps in the ionic strength-induced compaction. (C) Possible organization of the DNA within a metaphase chromosome. Six nucleosomes form each turn of a solenoid in the 30-nm filament as in (A). The 30-nm filament forms 30 kb-loop domains of DNA and some of these attach at the base to the nuclear matrix that contains topoisomerase II. About ten of the loops form a helical radial array of 250-nm diameter around the core of the chromosome. Further winding of this helix into a tight coil 700 nm in diameter, as at the top in (C), forms a metaphase chromatid. From Manuelidis91.

Pull glass filaments on Sutter Model P-87 (Program heat = 750, pull = 0, velocity = 20, time = 250, pressure = 100, loops 2 or 3 times) to achieve 2-3 pm needle diameter. 

A simple way of checking the variability of the filament diameter in a precursor tow is to use a polished stainless steel plate, which has been drilled with several countersunk holes to accommodate different precursor tow sizes (Figure 17.1). A looped needle threader is pushed... 

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