Distinct single-copy sequence sets in sea urchin nuclear RNAs.

The purpose of this study was to determine whether nuclear RNAs (nRNA) of sea urchin embryos and adult tissues contain identical or partially distinct sets of single-copy sequence transcripts. A DNA tracer was prepared consisting mainly of sequences absent from gastrula nRNA; 3.6% of this tracer reacted with adult intestine nRNA but not with gastrula nRNA. The existence of a differentially transcribed DNA fraction was verified by its partial purification and rehybridization to intestine and gastrula nRNAs. About one-third of the genomic single-copy sequence is represented in both nRNAs, or about 2 x 10(8) nucleotides. The differentially transcribed portion of the single-copy genome identified in this work includes about 3.5 x 10(7) nucleotides.