{HEAD ~ The presence} of {TAIL ~ the trpl lesion} as a characteristic of the yeast host cell genome than provides an effective environment for detecting transformation by growth in the absence of tryptophan 
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{ HEAD ~ The presence } of { TAIL ~ the trpl lesion } as a characteristic of the yeast host cell genome than provides an effective environment for detecting transformation by growth in the absence of tryptophan
HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH