Regarding Unknown Nucleic residues "N":  (See also UNK for unknown AAs.)

May 2024: PDB has 96 entries with N.    
	6 are in "Nucleic only". N13,14 in chain A in 7e9e as phosphoribose. cf 6e1w. 
	8 are in "Protein only" as ligands: "Any 5'-monophosphate nucleotide".  
	In 1g9s,1phw,3dzi(AU),8u0z, modeled as phosphoribose.   
	82 are in "Protein/NA".

1dva has a long chain of N's modeled as phosphoribose. Jmol.jar cannot render it as cartoon,
trace, backbone. I think this is because the absence of base atoms make these not