A convenient strategy to clone small RNA and mRNA for high-throughput sequencing

High-throughput sequencing has become a standard tool for analyzing RNA and DNA. This method usually needs a cDNA/DNA library ligated with specific 5′ and 3′ linkers. Unlike mRNA, small RNA often contains modifications including 5′ cap or triphosphate and 2′-O-methyl, requiring additional processing steps before linker additions during cloning processes; due to low expression levels, it is difficult to clone small RNA with a small amount of total RNA. Here we present a new strategy to clone 5′ modified or unmodified small RNA in an all-liquid-based reaction carried out in a single PCR tube with as little as 20 ng total RNA. The 7-h cloning process only needs ∼1 h of labor. Moreover, this method can also clone mRNA, simplifying the need to prepare two cloning systems for small RNA and mRNA; the barcoded PCR primers are also compatible with non-cDNA cloning applications, including the preparation of genomic libraries. Not only is our method more convenient for cloning modified RNA than available methods, but it is also more sensitive, versatile, and cost-effective. Moreover, the all-liquid-based reaction can be performed in an automated manner.