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By early 1977, I had fulfilled all degree requirements and demonstrated that discrete genetic elements such as promoters, ribosome binding sites, and coding sequences, could be arranged into new and functional combinations. It was apparent that genetic engineering would be a convenient route to obtain large quantities of proteins that were commercially valuable or otherwise scarce. Very shortly thereafter, the practical ability to synthesize DNA in vitro had a major impact on how genetic engineering was practised, as did the later developments of directed mutagenesis and PCR. The methods used in my experiments have become comparatively cumbersome and have now fallen into disuse. However, in the absence of such facilitating technologies as in vitro DNA synthesis and PCR, these methods were crucial for my experiments. To obtain DNA fragments containing defined elements, I had to wait for new restriction enzymes to become available. Even then, it was necessary to reconstruct the target gene from its halves, and to invent an ad hoc method of connecting different types of DNA fragment ends in a reversible manner.While I was doing this work, the cutting edge of what was possible changed on an almost daily basis. I was fortunate to work at the intersection of two important model systems, lac and λ, because sequence information for these systems was available shortly, but significantly, before similar information for other systems. Because of my fortuitous situation, and despite the technical challenges, I was able to perform the first genetic engineering experiments at my bench on the fourth floor of the Harvard University Biological Laboratories. |
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