Dr. Donald S. Frederickson 
- 2 - 
August 30, 1978 
"Human adenoviruses 2 and 5 rendered unconditionally defective by deletion 
of at least two essential genes, with appropriate helper, can be used in P3 
conditions to propagate DNA sequences from:" 
Thank you for the opportunity to comment on the revised guidelines. 
Daniel Nathans 
Professor and Director 
Department of Microbiology 
DN/lc 
[A-62] 
