miRT: A Database of Validated Transcription Start Sites of Human MicroRNAs

MicroRNAs (miRNAs) are small endogenous non-coding RNAs of about 22 nt in length that take crucial roles in many biological processes. These short RNAs regulate the expression of mRNAs by binding to their 3′-UTRs or by translational repression. Many of the current studies focus on how mature miRNAs regulate mRNAs, however, very limited knowledge is available regarding their transcriptional loci. It is known that primary miRNAs (pri-miRs) are first transcribed from the DNA, followed by the formation of precursor miRNAs (pre-miRs) by endonuclease activity, which finally produces the mature miRNAs. Till date, many of the pre-miRs and mature miRNAs have been experimentally verified. But unfortunately, identification of the loci of pri-miRs, promoters and associated transcription start sites (TSSs) are still in progress. TSSs of only about 40% of the known mature miRNAs in human have been reported. This information, albeit limited, may be useful for further study of the regulation of miRNAs. In this paper, we provide a novel database of validated miRNA TSSs, miRT, by collecting data from several experimental studies that validate miRNA TSSs and are available for full download. We present miRT as a web server and it is also possible to convert the TSS loci between different genome built. miRT might be a valuable resource for advanced research on miRNA regulation, which is freely accessible at: http://www.isical.ac.in/~bioinfo_miu/miRT/miRT.php.