= Jennifer A. Doudna
{c}
Jennifer A. Doudna studies <RNA>–<protein> systems and their roles in <gene expression>. She coauthored the 2011 <Xrn1> study with <Martin Jinek> and <Scott M. Coyle>, connecting recognition of an <RNA>'s $5'$ end with its processive degradation.<Coupled 5′ nucleotide recognition and processivity in Xrn1-mediated mRNA decay by Martin Jinek and others>[Byline and Summary]{ref}
Doudna also coauthored the 2012 biochemical demonstration that <Cas9> uses <RNA> guides for sequence-directed <DNA> cleavage. The study showed that a single engineered <RNA> could combine the guiding functions of the natural two-RNA system, establishing a basis for programmable <CRISPR genome editing>.<A programmable dual-RNA-guided DNA endonuclease in adaptive bacterial immunity by Martin Jinek and others>[Abstract and Figure 5]{ref}
The distinction between cutting a molecule and editing a <genome> is essential. Cleavage is an experimentally observed chemical event; the final inherited sequence additionally depends on <DNA repair> and cellular context. A nuclease result alone does not specify a repaired <allele>.
For an original geometric example, one complete double-strand cut in a circular <DNA> molecule opens it into one linear molecule. One internal double-strand cut in an already linear molecule instead gives two fragments. The same number of cuts can therefore yield different product counts depending on the starting topology. This elementary accounting illustrates why a <gel electrophoresis> result must be interpreted with a known starting <substrate>; it is not a numerical result from either paper.
\Image[https://mcb.berkeley.edu/sites/default/files/images/faculty/doudnaj_250_309.jpg]
{title=Jennifer A. Doudna, portrait by Keegan Houser linked from her Berkeley faculty profile}
{description=<Jennifer A. Doudna faculty profile at Berkeley>[Named portrait and photo credit]{ref}}
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