A convenient strategy to clone modified/unmodified small RNA and mRNA for high throughput sequencing

Abstract

The high-throughput sequencing has become a standard tool for analyzing gene expression. Usually a cDNA/DNA library is constructed with 5' and 3' linkers and then sequenced. Unlike mRNA, small RNA often contains modifications including 5' cap or triphosphate and 3' methylation, affecting the linker addition during cloning processes. Small RNA is expressed at much lower levels than mRNA, making it more difficult to clone small RNA using a small amount of total RNA. Here we have developed a new strategy to clone modified/unmodified small RNA in an all-liquid-based reaction in a single PCR tube using as little as 20 ng total RNA. The 7-hour cloning process only needs ~1 hour labor time. Moreover, this method can be used to clone mRNA, simplifying the need to prepare two cloning systems for small RNA and mRNA. Since the linkers used are derived from the Illumina Truseq linkers for DNA cloning, the PCR primers based on the linker sequences can be used to obtain amplicons derived from small RNA/mRNA/DNA. Not only is our method more convenient for cloning modified RNA than available methods, but it is also more sensitive, accurate and versatile. Moreover, the all-liquid-based reaction can be performed in an automated manner.