load =1DDN

delete HOH
delete Ni
delete *:A.*
define set1 *.O?' and dna
define set2 *.OP?
define set3 [DA]*:?.N? or [DG]*:?.N? or [DC]*:?.N? or [DT]*:?.N?
pause
resume

restrict DNA
cpk off
pause
resume

select set1
cpk 100
pause
resume

cpk off
select set2
cpk 100
pause
resume

cpk off
select set3
cpk 100