To make a helical filament three subunits long from a single subunit PDB 6g19 with rise of 46 Angstroms per turn and 76 degrees rotation per subunit I’ll use the ChimeraX sym command.
I want the axis of the filament aligned to the axis of the double stranded RNA, chains X and Y. To calculate this axis I open 2 copies of the structure, align the second copy RNA to the first copy RNA shifted by one nucleotide, then use the measure rotation command to get axis of the rotation that moves the first copy to the second copy.
open 6g19 open 6g19 align #2/X:1-13@P #2/Y:2-14@P to #1/X:2-14@P #1/Y:1-13@P measure rotation #1 to #2 sym #1 H,46,74,3 axis #3 copies true
Here is what this looks like:
I colored the RNA blue with command
color #4/X,Y cornflowerblue
I changed the subunit colors using the color buttons in the Models panel.
Tom Goddard, September 10, 2020