The nucleolar protein, B-36, contains a glycine and dimethylarginine-rich sequence conserved in several other nuclear RNA-binding proteins

The amino terminal sequence of the 34 kD nucleolar protein B-36 isolated from the slime mold Physarum polycephalum has been determined. This portion of B-36 is rich in glycine, phenylalanine and the modified amino acid asymmetrical dimethylarginine (DMA) and is 65% identical to that for fibrillarin, a similar and potentially homologous 34 kD nucleolar protein from rat. The terminus of B-36 contains an interesting nine amino acid sequence, Gly-DMA-Gly-Gly-Phe-Gly-Gly-DMA-Gly, which is precisely repeated three times in the 110 kD nucleolar protein nucleolin. Similar sequences have also been reported in a yeast nucleolar protein (SSB-1) and several hnRNP proteins (rat A1 and brine shrimp GRP33). The conserved nature of this unusual sequence is suggestive of an important function which may include RNA-binding since several of these proteins share this feature.