In a demonstration page for students, I wish to show how the presence of the 2’OH on a ribonucleotide creates a clash at the active site of DNA polymerase. We are also trying to see if 2’OH’s create clashes within the primer. I have created a PDB file with deoxyribose as alternative location A and ribose as alternative location B. This works in original Chimera, but I am not getting it to work in ChimeraX. I am not able to specify the alternative atoms by their A and B designations. I do not see alternative locations in the hierarchy under target specification in the documentation. My PDB file is attached. Residues 106-113 have alternate locations included. The command “altlocs change A :113" does not seem to change anything, nor does changing the selection buttons in the Altexplorer. Mike Bruist mbruist@sju.edu