FIGURE 3. Nucleoprotein crystal structure.
From the following article:
The mechanism by which influenza A virus nucleoprotein forms oligomers and binds RNA
Qiaozhen Ye, Robert M. Krug & Yizhi Jane Tao
Nature 444, 1078-1082(21 December 2006)
doi:10.1038/nature05379
a, Nucleoprotein trimer viewed along the NCS three-fold axis, with three subunits shown in different colours. The rotation angles that relate the three subunits are marked. b, Side view of a nucleoprotein trimer, with the three subunits coloured as in a. c, Nucleoprotein secondary structure assignment (subunit B). 
-Helices and 
-strands are shown by rods and arrows, respectively. -Strands with opposite signs form antiparallel -strands. d, Nucleoprotein subunit B. The polypeptide is coloured continuously from blue to red. Residues preceding and succeeding disordered regions are marked and connected by dotted lines.