14 
the language sinply state that shuttle vectors "constructed from vectors described 
in Appendix C" are permissible. Dr. Dean felt the language should be as general 
as possible and agreed with Dr. Baltz's suggestion. The working group agreed. 
Dr. Cchen asked whether the DNA of the phage vectors described in Appendix C 
might be included under the exemption. The working group thought this would 
be reasonable in order to permit use of cos mid vectors. They noted the term 
" extrachrcnosomal elements" includes phage vectors. 
Dr. Macrina asked hew a conjugative transposon that exists only on the chromo- 
some would be considered. Is it indigenous chromosomal material; if it can 
move to other organisms, would it be considered extrachrcnosomal? 
Dr. Clewell said conjugative transposons in gram-positive bacteria do not appear 
to transfer chromosomal genes. 
Dr. Cchen asked hew phage integrated into the chromosome would be handled under 
this proposal. Dr. Lovett offered the example of a defective temperate Bacillus 
subtilis bacteriophage which can replicate extrachrcnosomal ly when cloned in a 
recombinant minus (rec - ) bacteria. Dr. Macrina said clostridial plasmid probes 
hybridize to the DNA of plasmid- less Clostridia strains . These integrated 
plasmids apparently do not come out of the chromosome. He hypothesized inte- 
grated plasmids may occur widely in the understudied gram-positive organisms. 
The working group decided integrated plasmids, transposons, or phages which do 
not ccme out of the chromosome would not be considered extxachrcmosomal elements 
under this proposal. 
Dr. Thcmashow asked whether there is evidence of transfer of non-mobilizable 
plasmids by "conjugative-like" plasmids in gram-positive bacteria. Dr. Clewell 
said non-mobilizable plasmids are transferred by "conjugative-like" plasmids but 
the mechanism by which this occurs is not known. Dr. Macrina hypothesized 
seme of the non-mobilizable plasmids may be transferred by mob mechanisms; 
others may be transferred by co- integration into "conjugative-like" plasmids. 
Dr. Dean said there is extensive DNA homology between the plasmids and the 
transposons covered by the working group proposal. Dr. Lovett agreed; he 
offered the example of an apparently identical plasmid independently isolated 
from three different sources: the plasmid pAM-alpha-1 from Sj_ faecalis ; the 
plasmid pBC16 frem Bacillus cereus ; and the plasmid PUB110 frcm aureus . The 
high degree of homology observed in these plasmids suggests recent lateral 
transfer of the plasmid between these organisms. Dr. Macrina offered the 
example of two transposons which appear to be identical although isolated frcm 
different sources: the transposon TN917 isolated frcm an enteric Streptococcus 
and the transposon TN551 isolated frcm Sj_ aureus . 
The working group then began to construct the list of organisms which exchange 
broad host-range plasmids. They accepted most of the organisms listed by 
Drs. Novick and Polak in their proposal . 
[545] 
