Nijhawan P, Marzluff W F
Biochemistry. 1979 Apr 3;18(7):1353-60. doi: 10.1021/bi00574a035.
There are three major low molecular weight RNAs (150-300 nucleotides) larger than 5S rRNA present in sea urchin embryos. Two of these are localized in the nucleus and one is localized in the cytoplasm. The nuclear species contain "capped" 5' termini, with a cap I structure. These RNAs are synthesized starting in late cleavage and continuing through pluteus. Relative to 5S RNA there is a 10-fold change in the rate of synthesis of these RNAs, due primarily to a decrease in their rate of transcription after blastula. The RNAs are metabolically stable and the nuclear RNA genes are reiterated 50--100 times in the genome. Significant amounts of these RNAs are present in sea urchin eggs, enough to supply the embryo during early cleavage, prior to initiation of their synthesis.
海胆胚胎中存在三种分子量比5S rRNA大的主要低分子量RNA（150 - 300个核苷酸）。其中两种定位于细胞核，一种定位于细胞质。核内的这类RNA含有“帽化”的5'末端，具有帽I结构。这些RNA从卵裂后期开始合成，并持续到长腕幼虫期。相对于5S RNA，这些RNA的合成速率有10倍的变化，这主要是由于囊胚期后其转录速率下降所致。这些RNA在代谢上是稳定的，核RNA基因在基因组中重复50 - 100次。海胆卵中存在大量这些RNA，足以在其合成开始前的早期卵裂阶段为胚胎提供所需。
