Sequence complexity of nuclear RNAs in adult rat tissues

Abstract

The sequence complexity of nuclear RNA from adult rat tissues was measured by RNA-driven hybridization to iodinated single-copy DNA. Assuming asymmetric transcription, 31.2 ± 0.9% of the unique sequence DNA was represented in brain nuclear RNA; 21.8 ±1.2% in liver nuclear RNA; 10.6 ± 0.3% in kidney nuclear RNA; 9.6% in spleen nuclear RNA; and 9.2 ± 2.6% in thymus nuclear RNA. These are equivalent to RNA sequence complexities of 5.9 × 10 8 nucleotides for brain RNA; 4.1 × 10 8 nucleotides for liver RNA; 2.0 × 10 8 nucleotides for kidney RNA; 1.8 × 10 8 for spleen RNA; and 1.7 × 10 8 for thymus RNA. To estimate the degree to which nuclear sequences are shared between tissues, mixtures of two RNAs were annealed simultaneously to single-copy DNA. The mixture of brain and liver RNA hybridizes to the same extent as brain RNA alone; the mixture of liver and kidney RNA anneals to the same extent as liver RNA alone. This suggests that the great majority of nuclear RNA sequences homologous to single-copy DNA are held in common between these tissues and form a “nested” set of mutually inclusive sequences. An approximate calculation indicates there are between 1–3 copies per cell of the diverse class of nuclear RNAs in brain, liver and kidney.