AFM images of G ₁ -phase premature condensed chromosomes: Evidence for 30 nm changed to 50 nm chromatin fibers

To gain evidence for 30 nm changed to 50 nm chromatin fibers, we used atomic force microscopy (AFM) to study the ultrastructural organization of G ₁ -phase premature condensed chromosomes (PCC). The surface of early G ₁ -phase PCC is smooth and fibrous structures exist around the chromatids. The height of early G ₁ -phase PCC is about 410 nm and the width is 1.07 ± 0.11 μm (n = 30). At late G ₁ -phase, the surface becomes globular. The height of late G1-phase PCC is about 370 nm and the width is 845.04 ± 82.84 nm (n = 30). Phase image reveals that early G ₁ -phase PCC is composed of 50 nm (48.91 ± 6.63 nm, n = 30) chromatin fibers and these 50 nm chromatin fibers tangle together, while late G ₁ -phase PCC is composed of 30 nm (30.96 ± 4.07 nm, n = 30) chromatin fibers. At high magnification, fibers existing around the chromatids become clear in early G ₁ -phase PCC. Chromatin fibers revealed by closer view of the end of chromatid are about 50 nm. In late G ₁ -phase PCC, the surface presents globular structures. The shape of these globular structures is regular and the diameter is 118.96 ± 11.70 nm (n = 30). Our results clearly show that 30 nm chromatin fibers change to 50 nm chromatin fibers in G ₁ -phase PCC and suggest that 50 nm chromatin fibers are the basic component of the mitotic chromosomes.