TOWARD A RESOLUTION OF THE INTRONS EARLY LATE DEBATE - ONLY PHASE ZERO INTRONS ARE CORRELATED WITH THE STRUCTURE OF ANCIENT PROTEINS/

We present evidence that a well defined subset of intron positions sho ws a nos-random distribution ire ancient genes. We analyze a database of ancient conserved regions drawn from GenBank 101 to retest two pred ictions of the theory that the first genes were constructed by exon sh uffling. These predictions are that there should be an excess of symme tric exons land sets of exons) flanked by introns of the same phase (p ositions within the codon) and that intron positions in ancient protei ns should correlate with the boundaries of compact protein modules. Bo th these predictions are supported by the data, with considerable stat istical force (P values < 0.0001). Intron positions correlate to modul es of diameters around 21, 27, and 33 Angstrom, and this correlation i s due to phase zero introns. We suggest that 30-40% of present day int ron positions ire ancient genes correspond to phase zero introns origi nally present ire the progenote, while almost all of the remaining int ron positions correspond to introns added, or moved, appearing equally in all three intron phases. This proposal provides a resolution for m any of the arguments of the introns-early/introns-late debate.