RELATIONSHIPS BETWEEN GENOMIC G-GROWTH TEMPERATURE IN PROKARYOTES(C CONTENT, RNA SECONDARY STRUCTURES, AND OPTIMAL)

G:C pairs are more stable than A:T pairs because they have an addition al hydrogen bond. This has led to many studies on the correlation betw een the guanine+cytosine (G+C) content of nucleic acids and temperatur e over the last 20 years. We collected the optimal growth temperatures (T-opt) and the G+C contents of genomic DNA; 23S, 16S, and 5S ribosom al RNAs; and transfer RNAs for 764 prokaryotic species. No correlation was found between genomic G+C content and T-opt, but there were strik ing correlations between the G+C content of ribosomal and transfer RNA stems and T-opt. Two explanations have been proposed--neutral evoluti on and selection pressure--for the approximate equalities of G and C ( respectively, A and T) contents within each strand of DNA molecules. O ur results do not support the notion that selection pressure induces c omplementary oligonucleotides in close proximity and therefore numerou s secondary structures in prokaryotic DNA, as the genomic G+C content does not behave in the same way as that of folded RNA with respect to optimal growth temperature.