MicroRNAs are key regulators in diverse cellular pathways of
eukaryotes from cell differentiation to open development.
This presentation will explain what is known about these interesting molecules with
an emphasis on the gene structure, transcription, and processing.
Let me begin with the definition of microRNAs.
MicroRNA, miRNA for short is defined as
a single-stranded RNA of approximately 22 nucleotides in length,
which is generated by the RNAse III type enzyme from
an endogenous transcript that contains a local hairpin structure.
Shown here as examples are let-7 RNAs from C. elegans, Drosophila and human.
Highlighted in red is the mature let-7 RNA that is
processed out of one arm of the hairpin shaped precursor.
Like let-7 RNA, a number of microRNAs are conserved phylogenetically.
The degree of conservation is highest in
the mature microRNA segments but gets lower
in the terminal loop and in the base pair segments.
The length of the hairpin is approximately 85 nucleotides in animals.
But in plants, the structure and the length of the precursor is more variable.