SBIR-STTR Award

Microarrays are powerful tools that can impact new diagnostic procedures and expedite the drug development process. A significant but largely unrealized application is gene expression analysis from RNAlimited samples, such as blood, needle biopsies, laser capture microdissection (LCM) samples, and even single cells. The most widely used T7 RNA polymerase-based amplification method currenly lacks the necessary sophistication to meet these emerging needs. To overcome these limitations, we propose to increase the efficiency of T7 RNA amplification using an innovative protein engineering approach. Through combined rational design and random mutagenesis, mutant library selection and screening, we aim to identify a hyperactive T7 RNA polymerase that is 4-5 times more kinetically proficient than the current enzyme. We will expand this novel approach in phase II to include the discovery of mutant T7 polymerase enzymes that are both more thermostable (and thus extend high efficiency transcription for longer times, creating more product) and can incorporate biotinylated and Cy-modified nucleotides 5- to 10-fold more efficiently. Taken together, these improvements will lower the demand for input RNA by approximately 20-fold, and reduce the expense of modified nucleotides by as much as an order of magnitude

Expanding use of microarray systems for global gene expression profiling is leading biological research, providing diagnostic and prognostic value to physicians and facilitating target discovery during drug and vaccine development. There is strong interest in extending this microarray capability to more RNA-limited material to the point that a single cell can be profiled with confidence. The most widely used method for preparing samples for microarray analysis, which uses cDNA synthesis from mRNA followed by T7 RNA polymerase-based amplification, currently lacks the necessary sensitivity to meet these emerging needs. To overcome these methodological limitations, we propose to increase the final amplified RNA yield by 1) improving the efficiency of T7 RNA polymerase using structure-based engineering with directed evolution of function, 2) by optimizing the design of the promoter-template construct for specific amplification needs and 3) by re-standardization of cDNA synthesis for lower RNA inputs. The combined improvements are expected to lower the cell-limited RNA sample requirement by 100-fold compared to current, commercially available kits. This will enable microarray gene analysis with as little as 1 ng of total RNA with a single round of amplification or microarray profiling from a single cell (-10 pg of total RNA) after two rounds of amplification