Zintrons in rat alpha-lactalbumin gene

The eukaryotic genome is characterised by the occurrence of a large amount of repetitive DNA which exists within and around coding sequences. Random repeats of (TG)n sequences have been observed in several introns. In this paper we show that (TG)14 and (TG)24 sequences present in the third intron of rat alpha-lactalbumin gene adopt left-handed Z-helices under varying superhelical densities. The overall sequence of the parent plasmid further influenced the level of supercoiling at which the B to Z transition could be induced in (TG)n sequences. Such Z-potential intervening sequences (zintrons) could act as buffers to maintain desired levels of supercoiling near the transcribed sequences.