UCbase is a database of ultraconserved sequences (UCRs or UCEs) that were first described by Bejerano, G. et al.[2] in 2004.

They are highly conserved genome regions that share 100% identity among human, mouse and rat.

They are frequently located at genomic regions involved in cancer, differentially expressed in human leukemias and carcinomas and in some instances regulated by microRNAs.

[4] Recent updates include new annotation based on hg19 Human genome, information about disorders related to the chromosome coordinates using the SNOMED CT classification, a query tool to search for SNPs, and a new text box to directly interrogate the database using a MySQL interface.

UCbase 2.0 does not provide microRNAs (miRNAs) information anymore focusing only on UCRs.