4 
Dr. Friedman suggested the working group not attempt at this meeting to rewrite 
the philosophical underpinnings of the NIH Guidelines; he thought it would be 
sinpler for the working group to operate within the existing historical context. 
Dr. Milewski suggested the working group first evaluate the proposal submitted 
by Drs. Novick and FOlak. If the working group feels it is appropriate, the 
working group might proceed to develop a motion to modify the NIH Guidelines 
or to discuss the criteria for exemption under Section III-D-4. 
Dr. Clewell suggested the working group for the moment accept the historical 
context and evaluate the proposal submitted by Drs. Novick and Polak. 
Dr. Maori na commented that the working group may wish to consider the importance 
of tranductional, con jugat ional , transpositional, and transformational exchange 
in considering chromosomal gene exchange. 
Dr. Friedman did not think it irrportant to describe the mechanism of transfer; 
rather the working group should simply consider whether transfer of genetic 
material occurs. 
Dr. Baltz asked whether organisms can be added to Appendix A sublists on the 
basis of DNA horology. He said most Streptcmyces species are closely related. 
On the basis of 23s riboscmal FNA (rFNA) homology, seme investigators suggest 
all Streptcmyces species cure probably one and the same species. 
Dr. Macrina thought DNA horology alone would not be a good criterion on which 
to add organisms to Appendix A. The numbers can be misleading as can be seen 
by comparison of sequence data and DNA hybridization data. For example, seme 
genes are 40 to 50% homologous at the sequence level but do not hybridize even 
under lew stringency conditions. On the other hand, horology in certain genes 
under standard DNA/DNA hybridization methodology can be quite high between 
phy logenetical ly distant species. 
Dr. Fox said molecular taxonomists would argue ENA hybridization numbers in the 
latter case are meaningless; the important numbers in determining relatedness 
sure sequence data on 23s riboscmal ENA. The highly conserved nature of rFNA 
ENA makes rRNA sequence homology a useful tool for investigating the relation- 
ships of ply logenetical ly distant organisms but it ceases to be useful for 
investigating relatedness in closely related organisms. Closely related 
organisms can show very high degrees of rFNA hybridizibility but display very 
different characteristics. Eh_ coli and Salmonella , for example, display different 
biological behavior but possess essentially identical rFNA sequences. Thus, 
rFNA sequence relatedness studies indicate whether organisms are related 
tut not whether the organisms would be classified within a species or gerus. 
For example, B^_ subtil is and the Mycoplasmata possess very similar rRNAs but 
they are not classified within the same gems. A good method of using rFNA 
sequence homology data for taxcmonic classification has not yet been developed. 
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