Phillip Allen Sharp (1944 - present) shared the 1993 Nobel Prize in Physiology or Medicine with Richard J. Roberts for his independent discovery that individual genes are often interrupted by long sections of DNA that do not encode protein structure. Sharp and his team discovered that the messenger RNA (mRNA) of an adenovirus corresponded to four separate, discontinuous segments of DNA. These coding segments, called exons, were separated by long stretches of DNA, called introns, that did not contain genetic information. Previously it was believed that genes were continuous stretches of DNA that served as direct templates for mRNA in the assembly of proteins. Subsequent studies -- many of them carried out in Sharp's laboratory -- showed that DNA transcription initially produces a precursor RNA molecule from which the introns are removed and the exons are spliced together.