Y3 is the Most Conserved Small RNA Component of Ro Ribonucleoprotein Complexes in Vertebrate Species

YRNAs are small cytoplasmic RNAs that are components of the Ro ribonucleoprotein complex. This complex, which also includes the 60-kDa Ro protein, is a human autoantigen which is conserved among vertebrates, and is of unknown function. Multiple sequences with YRNA homology, known as YRNA-like sequences, have been detected in rabbit, mouse, duck, iguana and frog genomes with human Y cDNA probes. As judged by Northern blots of total RNA, however, not all of these genomic YRNA-like sequences are expressed. Complementary DNA and putative gene sequences for iguana Y3 (iY3) and iguana Y4 (iY4) Ro RNAs have been determined and used, along with previously sequenced human and frog Ro YRNA sequences, to construct the most likely Y3 and Y4 RNA secondary structures. The data presented indicate that Y3 is the most conserved Ro RNA, not only by its more consistent presence in other species, but also at the levels of sequence divergence and secondary structure similarity. The differences observed between the secondary structure solutions for the Y3 and Y4 Ro RNAs are consistent with the possibility that these RNAs perform different cellular functions.