Transcriptional and structural study of a region of two convergent overlapping yeast genes

The exceptionally close packing of many yeast genes and other chromosomal e lements raises the question of how those elements are functionally insulate d. All published work shows that natural insulators are very effective, but transcriptional interference (TI) occurs if they are mutated or if their n atural context is altered. Mechanisms to avoid TI are poorly understood, bu t are thought to involve an interplay of cis sequences and trans factors in a chromatin context. We have studied the case of two convergent closely pa cked ORFs (56 bp of separation) in chromosome IX of Saccharomyces cerevisia e. mRNAs from POT1 and YIL161w overlap by up to 115 nt. Convergent transcri ption causes a small but noticeable negative effect on the level of POT1 mR NA and nucleosome displacement in the intergenic region. This suggests for the first time that some TI could occur in convergently transcribed yeast g enes, even in a natural chromosomal context.