NONUNIFORM DISTRIBUTION OF INTRON PHASE FREQUENCY

The phase frequency distribution of introns of different groups was ex amined. Group II and nuclear introns were found to have the same minim um of phase 2 relative frequency. Since the intron phase is an extreme ly conservative index, the observed minimum is a trace of relict evolu tionary processes. The sample of all known group I introns proved insu fficient for obtaining a valid characteristic of phase distribution. I t was shown that the phase distribution pattern observed could not be interpreted basing solely on the mobile properties of introns. A plaus ible explanation for the nonuniform intron phase distribution is exon shuffling. It is suggested that group II and nuclear introns originate d from the ancient introns which existed before the divergence of pro- and eukaryotes, and that both groups were actively involved in exon s huffling.