8 
to synthesize the mucopolysaccharide colanic acid which can facilitate the 
ability of E. coli to survive in the absence of the raureir. layer of the 
cell wall, is sensitive to bile salts and detergents, undergoes thymineless 
death and degrades its DNA in environments lacking thymine- or thymidine, 
is resistant to a number of E. coli transducing phages, is very sensitive 
to ultraviolet light irradiation, is unable to act as a recipient in 
matings with donors possessing conjugative plasmids in five of the groups 
commonly or occasionally found in enteric microorganisms and is defective 
as a recipient in matings with donors possessing other corjugative 
plasmid types." 
The present report contains an analysis and critique of the EK-2 
strain proposed by Curtiss and co-workers as described in their paper 
"Construction. Properties and Testing of XL776." The summary and 
conclusions presented in Section 1 of this report as well as the following 
comparison of the properties of xl?76/xl876 with the NIH Provisional 
Guidelines specifications for an EK-2 host have been prepared in order 
to make our criticisms directly accessible to those unfamiliar with 
the terms and concepts used in the technical analysis, which we present 
in a separate section (Section IV). 
[Appendix C — 196] 
