15 
Slide 2 
ErtdonuclMM 
5 = 
X txonuclMM 
dATP Terminal Troneftrote dTTP 
DNA polymero*# + 4dTP 
DNA IlgoM -I- DPN 
ExonuclMM II 
(dAM 
GO 
(<n> 
This method has several advantages, and is in fact being used in a 
number of laboratories to produce quite interesting types of molecular 
hybrids. Nevertheless, at the time it was reported, it was not widely 
adopted because it requires a number of special enzymes that are scarce, 
and also skills that are not widely practiced in many laboratories. 
As so often happens, however, a simpler procedure to accomplish the 
same and more was found. Several years ago, Dr. Herbert Boyer and his 
colleagues at the University of California Medical Center in San Francisco 
isolated an enzyme that can break the DNA into small bits. These pieces 
vary in length, but they are large enough to contain from one to ten genes. 
Two Stanford biochemistry colleagues, Janet Mertz and Ronald Davis, estab- 
lished that the enzyme breaks the DNA in a special way. This was a unique 
finding because the break leaves very characteristic sticky ends on these 
bits of DNA. 
[156] 
