Charmm22 force field for DNA

[songyunlong <songyunlong \\at// 263.net>]

Dear Computational Chemsitry Listers:
 Recently,I met with a difficult problem.I want to run a MCSS job to investigate
 the active site of a protein-DNA complex.However,the MCSS job requires the force
 field must be charmm22 force field. Then I assign the charmm22 force field to
 the protein-DNA complex,however,some nitrogen atoms of DNA,such as N3,N7, are
 not parameterized by charmm22 force field.I wonder whether DNA has been
 parameterized by charmm22 force field.In my opinion,as a famous macromolecular
 force field,CHARMM should have parmaterized for DNA as well as protein.How can I
 settle this problem?
 How can I parameterize DNA with charmm22 force field? Could you please kindly
 give me any suggestions on this problem?
 Best wishes to you!
 Song Yunlong,Ph.D
 ~~~~~~~~~~~~~~~~~~~~~~~~~~
 Dept of med chem
 School of pharmacy
 Sec Mil Med Univ
 Guohe Road,325
 Shanghai,200433
 E-mail:songyunlong \\at// 263.net
 ~~~~~~~~~~~~~~~~~~~~~~~~~~