APPENDIX A 
5 
D. Site-specific endonucleases 
Recently two restriction modification systems have been observed 
between B_. subtil is 168 and other bacilli. Trautner et aj_. have isolated 
an effective system that inhibits infection of the R strain of B_. subti 1 i s 
by bacteriophage SPP1 propagated on B_. subtil is 168 (27). The site- 
specific nuclease recognizes the sequence GGCC. Young, Radnay, and Wilson 
CCGG 
observed a restriction modification between B_. amyloliquefaciens and B_. 
subtil is 168 (28). The endonuclease from B_. amyl ol iquefaciens (20) recog- 
nizes the sequence GGATCC (29). More recently, two additional enzymes have 
CCTAGG 
been isolated from B_. globigii (30). The recognition sequence is not known. 
E. Advantages and liabilities of the B. subtilis system 
a. Advantages 
1. B_. subtilis is nonpathogenic. Asporogenic deletion mutants 
are available to preclude the problem of persistence through sporulation. 
2. The circular chromosomal map is well defined. At least 196 
loci have been positioned. 
3. The organism is commercially important in the fermentation 
industry. 
4. Large numbers of organisms can be disposed of readily with 
minimal environmental impact. 
5. Unlike E_. col i , it lacks endotoxin in the cell wall. Therefore 
the cells can be used as a single cell protein source. 
6. The frequency of transformation is very high, facilitating the 
detection of rare events. 
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