Introduction: MicroRNAs (miRNAs), which are evolutionarily conserved, and endogenous
non-coding RNAs, participate in the post-transcriptional regulation of eukaryotic genes. The biogenesis
of miRNAs occurs in the nucleus. Then, in the cytoplasm, they are assembled along with some proteins
in a ribonucleoprotein complex called RISC. miRNA component of the RISC complex binds to the
complementary sequence of mRNA target depending on the degree of complementarity, and leads to
mRNA degradation and/or inhibition of protein synthesis. miRNAs have been found in eukaryotes and
some viruses play a role in development, metabolism, cell proliferation, growth, differentiation, and death.
Objective: A large number of miRNAs and their targets were identified by different experimental
techniques and computational approaches. The principal aim of this paper is to gather information
about some miRNA databases and web-based tools for better and quicker access to relevant data.
Results: Accordingly, in this paper, we collected and introduced miRNA databases and some webbased
tools that have been developed by various research groups. We have categorized them into different
classes including databases for viral miRNAs, and plant miRNAs, miRNAs in human beings,
mice and other vertebrates, miRNAs related to human diseases, and target prediction, and miRNA expression.
Also, we have presented relevant statistical information about these databases.