Ca. Obrien et al., XENOPUS RO RIBONUCLEOPROTEINS - MEMBERS OF AN EVOLUTIONARILY CONSERVED CLASS OF CYTOPLASMIC RIBONUCLEOPROTEINS, Proceedings of the National Academy of Sciences of the United Statesof America, 90(15), 1993, pp. 7250-7254
Ro small ribonucleoproteins consist of a 60-kDa protein and possibly a
dditional proteins complexed with several small RNA molecules. The RNA
components of these particles, designated Y RNAs, are about 100 nt lo
ng. Although these small ribonucleoproteins are abundant components of
a variety of vertebrate species and cell types, their subcellular loc
ation is controversial, and their function is completely unknown. We h
ave identified and characterized the Ro RNPs of Xenopus laevis. Three
of the four distinct Xenopus Y RNAs appear to be related to the previo
usly sequenced human hY3, hY4, and hY5 RNAs. The fourth Xenopus Y RNA,
xYalpha, does not appear to be a homologue of any of the human Y RNAs
. Each of the human and Xenopus Y RNAs possesses a conserved stem that
contains the binding site for the 60-kDa Ro protein. Xenopus and huma
n 60-kDa Ro proteins are 78% identical in amino acid sequence, with th
e conservation extending throughout the entire protein. When human hY3
RNA is mixed with Xenopus egg extracts, the human RNA assembles with
the Xenopus Ro protein to form chimeric Ro ribonucleoproteins. By anal
yzing RNA extracted from manually enucleated oocytes and germinal vesi
cles, we have determined that Y RNAs are located in the oocyte cytopla
sm. By examining the distribution of mouse Ro ribonucleoproteins in cy
toplast and karyoplast fractions derived from L-929 cells, we have det
ermined that Ro ribonucleoprotein particles also primarily reside in t
he cytoplasm of mammalian cells.