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

The exceptionally close packing of many yeast genes and other chromosomal elements raises the question of how those elements are functionally insulated. All published work shows that natural insulators are very effective, but transcriptional interference (TI) occurs if they are mutated or if their natural context is altered. Mechanisms to avoid TI are poorly understood, but 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 packed ORFs (56 bp of separation) in chromosome IX of Saccharomyces cerevisiae. mRNAs from POT1 and YIL161w overlap by up to 115 nt. Convergent transcription causes a small but noticeable negative effect on the level of POT1 mRNA and nucleosome displacement in the intergenic region. This suggests for the first time that some TI could occur in convergently transcribed yeast genes, even in a natural chromosomal context.