Appeal No. 1999-1367
Application 08/453,998
galactosidase in yeast.” To understand the metes and bounds conferred by this recitation,
we turn to an analysis of claim construction for claim 25 as a whole.
Claim 25, part (i), recites a yeast cell transforming step, and defines the DNAs
introduced into yeast cells. Part (i)(a) defines the ligand responsive element. Part (i)(b)
defines the receptor. Steps (ii) and (iii) concern inducing expression and recovering
protein.
First, construction of part (i)(b). The DNA encoding the receptor has to be under the
control of elements providing for expression in yeast. The receptor is a natural nuclear
receptor for steroids or retinoids or thyroid hormones or vitamin D3, or is a variant of “said
receptors which retain the function of said receptors in yeast.” The receptor comprises a
first fragment that recognizes the ligand, and a second fragment that binds to the
transcriptional control sequence. One point for interpretation is what is meant by “the
function of said receptors in yeast.” Is “the function of said receptors” to bind the natural
ligand-responsive DNA sequence, or is it more broadly to bind any responsive DNA
sequence? Since the function of the natural receptor is two-fold, to bind the natural ligand
and to bind the natural ligand-responsive element, we interpret “the function” as meaning
the function of binding both the natural ligand and the natural ligand-responsive element.
This is consistent with the treatment in the specification, which distinguishes between
“natural” receptor and “hybrid” or “chimeric” receptor proteins (e.g., page 6, lines 9-16, and
26-27), where an example of the latter has a ligand-binding portion of higher eukaryotic
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