Various scenarios exist for the origin of RNA-based life forms that preceded the current largely protein-based life forms – hot-start versus cold- or warm-start, acidic versus basic pH – but little is known about the effects of high pressure on the chemical stability of nucleotides and the physical stability of folded functional RNA, which had both information storage and catalytic functions. In particular, cytidine hydrolyses to uracil at a measurable rate at elevated temperatures and ambient pressure, and folded RNA molecules, such as tRNA, unravel at mildly elevated temperatures.

Here, using a special cell and rig, we have examined by NMR spectroscopy the chemical stability of cytosine and cytidine at 100 oC as a function of pressure. By means of Next-Gen sequencing, the sequence-specific susceptibility to hydrolysis of cytosine in bacteriophage DNA, in circular double-stranded, single-stranded and linear forms, has been explored as a function of temperature, pressure and time.

We also examined by NMR spectroscopy the melting temperatures, residue-by-residue, of self-complementary hexamers and dodecamers of DNA, the latter with varying cytosine content ranging from 16.7% to 83.3% over the pressure range 0.1 MPa to 200 MPa. Remarkably, the oligomers did not necessarily melt from the ends. A tentative interpretation has implications for gene expression.

Next-gen sequencing of bacteriophage DNA subjected to various regimes of temperature and pressure has revealed marked adjacency effects on cytidine deamination.