The complete nucleotide sequence of the rat 18S ribosomal RNA gene and comparison with the respective yeast and frog genes

The complete nucleotide sequence of the rat 18S ribosomal RNA gene has been determined. A comparison of the rat 18S ribosomal RNA gene sequence with the known sequences of yeast and frog revealed three conserved (stable) regions, two unstable regions, and three large inserts. (A,T)→M(G,C) changes were more frequent than (G,C)→ (A,T) changes for three comparisons (yeast→ frog, frog→ rat, and yeast → rat). GC pairs were inserted preferentially over AT pairs for the same three comparisons. These two factors contribute to the progressively higher GC content of 18S ribosomal RNA of yeast, frog, and rat.