Codons and nearest-neighbor nucleotide pairs in mammalian messenger RNA.

The codons in four mammalian messenger RNAs (rabbit beta hemoglobin, rat pre-proinsulin, rat pre-growth hormone and human chorionic somatomammotropin) show a predominance of C and G in third nucleotide positions. The C:U ratio is about 2 to 1, and the G:A ratio is about 4 to 1. The possibility is discussed that this disproportionally resulted from DNA replicative errors that favor C.G pairs over A.T pairs, as found in the E. coli mut T strain. "Nearest neighbor" base pairs ("doublets") in the protein-coding regions of phiX174 and in four mammalian mRNAs have been compared. Mammalian mRNA has a low content of CpG in comparison with expectations from its C and G content.