Annotation of 390 bovine miRNA genes by sequence similarity with other species.

MicroRNAs (miRNAs) are small noncoding RNA molecules that negatively regulate the expression of many protein-coding genes by affecting the degradation rate of the mRNAs or the correct translation of the gene products. miRNAs are normally encoded in pre-miRNA sequences with lengths of approximately 70 nt; these in turn are processed into mature sequences of about 22 nt. In the latest ENSEMBL release of the cow genome (http://www.ensembl.org/Bos_taurus), there are 524 identified miRNA genes, but only 117 are annotated in MIRBASE (http://microrna.sanger.ac.uk/) with unique identifiers. The remaining 407 miRNA genes are annotated as novel genes by the ENSEMBL annotation pipeline. We investigated this last group of sequences, which are predicted pre-miRNA-encoding genes for which corresponding bovine miRNAs have not yet been identified. A similarity search approach was used to identify homologous sequences among the miRNAs annotated in other species.