5 
Riboscmal sequence hanology is a good method for investigating relationships 
between genera, but it is not obvious how rRNA homology could be applied to 
species definitions. 
Dr. Fox added that rRNA sequence homology of the Streptcnyces is quite high? 
perhaps in the 90% range. For comparison, the rRNA sequence homology between 
the Myccplasmata and Ih_ subtilis is probably in the 80% range. 
Dr. Baltz said he might independently attempt to develop a proposal to exempt 
experiments involving the Streptcmyces from the NIH Guidelines under Section III- 
D-4. He said the Streptcmyces have been exempted by the British Genetic Manipu- 
lation Advisory Group (GMAG ) from their guidelines. He felt a proposal to 
create an Appendix A sublist for Streptcmyces which addresses the issues would 
be accepted by the Recombinant DNA Advisory Committee (RAC) and the NIH. 
He said in addition to a high level of DNA homology, conjugation in Streptcmyces 
was demonstrated in the 1950s, and a number of plasmids cure known which mobilize 
chromosomal genes. 
Dr. Friedman called the attention of the working group to the first set of 
organisms proposed as exchangers of genetic information by Drs. Novick and 
Polak (Attachment II): Ih_ cereus and fh_ thuringiensis . 
Dr. Clewell asked whether Eh_ thuringiensis is a B. cereus strain vhich has 
acquired the capacity to produce the crystal protein toxin. Dr. Thome said 
it is very difficult to distinguish Bj_ cereus strains from B^ thuringiensis 
strains lacking the crystal protein plasmid. B^_ cereus and Ih_ thuringiensis 
share a high degree of ENA homology (>_ 90%). 
Dr. Thome said investigators have successfully transferred chrcmoscmal genes 
by transduction between seme B^ cereus and B^ thur ingiens is strains. However, 
among other Eh_ thuringiensis and Eb_ cereus strains, chromosomal gene transfer 
by transduction cannot be demonstrated. Why the transferred ENA does not 
integrate into the chromosome in seme strains is not known. 
Dr. Clewell asked whether Bj_ cereus and Ih_ thurgiensis exchange chrcmoscmal 
genes through plasmid association. 
Dr. Thome said "con jugative- like " plasmids transfer in both directions between 
B. cereus and thuringiensis ; chromosomal gene transfer by these "conjugative- 
like" plasmids has not yet been demonstrated. However, the EL_ thuringiensis 
crystal protein gene can be transferred by the "conjugation-like" mechanism; 
and there is evidence suggesting the crystal protein gene can be integrated 
into the chromosome. 
Dr. Dean said most of the crystal protein genes of Eh_ thuringiensis strains 
are carried on plasmids. Sane crystal protein genes are chromosomal ly located. 
There is strong homology between the plasmid-borne and chromosomal crystal 
protein genes, and the gene can probably jurrp from the plasmid to the chromosome. 
Inverted repeat sequences surround the crystal protein genes and integration 
is assumed to occur by this mechanism. Exchange between Bj_ thuringiensis , B. 
[536] 
