Scientific work (yeast nitrogen metabolism and gene regulation)

Chisholm’s published research (largely with T. G. Cooper) focused on regulation of the allantoin/urea catabolic pathway in Saccharomyces cerevisiae, especially transcriptional control of DUR1,2 (urea amidolyase) and the effects of mobile genetic elements on gene expression:

Constitutive allantoin-pathway mutants (1982): Identified and characterized mutants that constitutively produce the allantoin-degrading enzymes, helping establish the role of DAL80 as a negative regulator and clarifying induction/repression logic for the pathway.

cis-Dominant DUR1,2 upregulation (1984): Described cis-dominant mutations that dramatically enhance DUR1,2 expression while leaving normal induction and nitrogen catabolite repression intact—evidence for promoter-proximal control elements modulating urea amidolyase expression.

Discovery of a repeated DNA element, tau (1984): Reported tau, a 371-bp repeated element in yeast with inverted repeats, adding to the catalog of repetitive elements (alongside sigma/delta) that influence genome structure and transcription.

Ty retrotransposon effects on DUR1,2 (1992): Showed that Ty insertions upstream vs. downstream of native DUR1,2 promoter elements generate distinct expression patterns (enhanced yet regulated vs. ROAM-type deregulation), directly linking transposable-element position to regulatory outcomes.

These works are frequently cited in later syntheses of yeast nitrogen regulation and urea/amidolyase genetic