had conserved precursor structures furthermore six of the mirna candidates showed significant homology to the mature mirna sequence of known mirnas although these observations provide support for evolutionarily conserved novel mirnas they should not be used to exclude the remaining tags as legitimate mirnas because a significant number of recently reported human mirnas lack homology to species other than primates 5 second 81 of the novel candidate mirnas were represented by more than one mirage tag or were independently detected in additional samples by using either mirna microarrays 5 19 table 6 which is published as supporting information on the pnas web site or quantitative real time pcr table 7 and fig7 which are published as supporting information on the pnas web site third 15 of the candidate mirnas were localized to genomic clusters of two or more mirnas separated by an average distance of 10 kb fig2 this physical proximity is consistent with recent reports of mirnas clustering within the human genome 20 fourth identification of a corresponding mirna sequence with characteristic 3 u2032 overhangs to a particular mirna is a strong indicator that the small rna species in question was processed by an rnase iii enzyme such as dicer mirna tags were observed for 12 of the candidate mirna sequences in total 89 of the 133 novel candidate mirnas had at least one independent piece of supporting evidence buttressing their legitimacy fig3 as a separate experimental.