Fig. 1.

Observation of MyBP-C in sectioned muscle. (A) Electron micrograph of frog sartorius muscle A-band prepared by fast-freezing/freeze-substitution (20). Transverse stripes of 43 nm periodicity (numbered 1–11) are due to MyBP-C and other nonmyosin proteins, and fine lines of 14.3 nm repeat are due to myosin heads. For ease of description, the numbering at 43 nm intervals is continued beyond stripe 11, although there are no nonmyosin proteins at these positions. Layer lines in the Fourier transform (inset; third and sixth marked) indicate good preservation of myosin head helical order. See also Fig  S1. (B) Mean profile plot of several boxed regions similar to that in (A). M, M-band; stripe 1 to 5, P-zone; stripe 5 to 11, C-zone; and stripe 11 to edge of A-band, D-zone. (Scale bar, 200 nm).