Team:HKU-Hong Kong/Project

In eukaryotes, heterochromatin plays an important role in gene regulation. Here we use a synthetic biology approach to imitate heterochromatin in E.coli to achieve gene silencing. Specifically, fusion proteins comprising tetR and different parts of HNS (histone-like nucleoid structuring protein) were synthesized, they are expected to bind DNA specifically and carry out polymerization among the fusion HNS and the native HNS to create a densely packed DNA form, which may block the transcription. We produced constructs with tetO sites upstream or downstream of lac promoter and EGFP gene. Then we used standard constitutive promoters with different activity to drive our fusion proteins to find the optimum expression level. Moreover, tetR, HNS and fusion proteins were purified and gel shift assay would be utilized to detect the interaction between those proteins with DNA. This study presents a novel approach to introduce a mimic heterochromatin-like structure into prokaryotes to achieve inducible gene silencing.

Gene silencing is not observed in bacteria in nature; however, the ability to knockdown the transcription of specific genes promises an attractive tool for bacterial reverse genetics, not to mention further possibilities of ‘silencing’ toxin-encoding genes in many pathogenic bacteria.

It is therefore of our interest to mimic this phenomena in E.coli by developing an ‘alternate’ mechanism using synthetic biology approaches. Our project attempts to test this by making use of the gene-repressing properties of a naturally-occurring protein in many gram-negative bacteria: the nucleoid protein H-NS. Fusion proteins with the H-NS domain were constructed and transformed into GFP-expressing E.coli. We engineered sites for the binding of these fusion proteins so that their binding can facilitate the repression of the GFP gene. To optimize the repression effect, we engineered the sites at different locations and also constructed fusion proteins with different H-NS domains and observed its effect in repressing GFP expression.

In this project we:

1. Created a total of eight BioBricks
2. Showed the possibility of silencing specific genes using fusion protein constructs and engineered DNA sequences