 U. Gubler

U. Gubler is first author, with B. J. Hoffman, of a 1983 method for generating cDNA libraries from small amounts of messenger RNA. The method combined first-strand synthesis with second-strand synthesis mediated by Ribonuclease H and DNA polymerase I.^[ref] This contribution made information in an RNA population accessible through recoverable DNA copies. The published initial is retained without assuming an expanded identity.

A cDNA library represents the RNA molecules successfully copied and recovered, rather than automatically representing every gene equally. Reverse transcription, second-strand synthesis and subsequent recovery can change representation. A useful library therefore requires more than a high total number of clones: rare transcripts and full-length products must also be considered.

An original sampling calculation isolates the rare-transcript question. Suppose a target transcript has probability $p=0.01$ in each independent recovered clone. The probability that $n$ examined clones contain no target isFor $n=80$, this is about 0.448. Requiring at least 95 percent probability of finding one target givesso at least 299 clones are needed under the stated independent-sampling model. Copying bias that lowers the recovered target fraction changes that calculation even if the starting RNA fraction was known.

The primary method paper also tested fidelity against a known transcript sequence.^[ref] Representation, product length and sequence agreement are distinct measurements. A large library can still undersample a rare transcript or contain truncated copies; neither conclusion follows from clone count alone.