Synthetic Biology Parts, Devices and Applications

118 6 Constitutive and Regulated Promoters in Yeast

copies; in most cases, a linear relationship is observed [90, 99, 102–104]. The

activity of promoters also depends on the spacer sequences placed between regu-

latory elements [59, 88, 105, 106]. These sequences can have an impact on the

efficiency of nucleosome clearance [43, 96]. Homopolymeric dA:dT or dG:dC

stretches disfavor nucleosome formation, thereby increasing transcription initia-

tion efficiency [44]. On the contrary, DNA sequences containing dA:dT dinucleo-

tides alternating with dG:dC dinucleotides are wrapped very efficiently into

nucleosomes, thereby inhibiting transcription initiation efficiency [43]. Therefore,

it is possible to fine‐tune initiation efficiency by modulating the length, composi-

tion, and location of dA:dT or dG:dC stretches within the promoter [44, 45].

Finally, it is also necessary to avoid the formation of structures that may have an

unpredictable influence on the promoter performance. For example, placing a

transcriptional terminator‐like sequence between the upstream element and the

core promoter can depress transcription initiation [107].

Core promoters TFBSs + cognate transcription factors

Combine

One regulator

Multiple regulators

Modify TFBS copy number

Figure 6.2 Synthetic hybrid promoters are obtained by combining a core promoter and one

or more transcription factor binding sites (TFBSs). Each TFBS is specifically recognized by a

transcription factor. By selecting the TFBSs, it is possible to choose which regulation the

synthetic hybrid promoter should display. The combination of two or more different TFBSs

results in a combinatorial regulation. The multiplication of the TFBS copy number results in

the adjustment of the promoter strength.