Homo sapiens U73b C/D box snoRNA. This snoRNA was characterized by Rebane et al. (1998) as a conserved sequence in intron 3 of the RPS3a gene. Its expression could not be evidenced in 4 cell lines by Northern blot and primer extension analyses, although its murine orthologue was detected in mouse cells. Compared to human U73a, and to murine U73a and U73b, a G-A substitution alters the base-pairing with 28S rRNA. Therefore, human U73b is considered as a pseudogene. U73b and U73a share the same host gene.