Tianyi Guan

About

This project investigated regulatory variation in the Escherichia coli lac operon by integrating phenotypic, biochemical, protein-level, and genotypic evidence. Wild-type and mutant strains affecting lacI or lacZ were examined under defined carbon-source and inducer conditions to determine how changes in repression and β-galactosidase function alter inducible gene expression. Complementary assays were used to resolve unknown strain identities and evaluate whether independent experimental readouts converged on consistent regulatory phenotypes.

Research Focus

To determine whether wild-type, lacI−, and lacZ− regulatory states can be distinguished through convergent phenotype-, enzyme-, protein-, and DNA-level evidence.

Study Design

Unknown E. coli strains representing wild-type, lacI−, or lacZ− genotypes were evaluated under control, glucose, lactose, and IPTG conditions. Lac operon activity was first assessed through ONPG-based β-galactosidase measurements and X-Gal phenotyping. Protein-expression profiles from uninduced and IPTG-induced cultures were subsequently compared by SDS-PAGE, while colony PCR targeting lacZ and lacI followed by agarose gel electrophoresis provided genotype-level evidence. Results across these assays were integrated to characterize regulatory behaviour and resolve strain identity.

Key Methods

Bacterial culture and induction; ONPG β-galactosidase assay; OD₄₂₀ / OD₅₅₀ spectrophotometry; X-Gal phenotyping; SDS-PAGE; Coomassie staining; colony PCR; agarose gel electrophoresis; genotype–phenotype integration;

Keywords

Escherichia coli; lac operon; gene regulation; lacI; lacZ; β-galactosidase; ONPG; X-Gal; SDS-PAGE; colony PCR; agarose gel electrophoresis;