Intergenic mRNAs. Minor gene products or tools of diversity?

Abstract

The general model of gene e x p r e s s i o n implies that the units of genetic information, the genes, constitute the basis of the mRNA and protein products detected in living organisms. It is well known that in eukaryotic cells a single gene may give rise to va r i o u s gene products due to alternative splicing and/or different positions of transcriptional start and termination. H ow eve r, recent experimental results suggest that in addition to this variation in gene expression, another l evel of complexity may also exist as evidence for the presence of mRNAs that combine sequence information ( exons) from distinct genes is accumulating. Moreove r, the mechanisms that allow this production of intergenic mRNAs are starting to unravel and it appears that these f o l l ow two general pathways: (a) bypass of transcriptional termination, resulting in the generation of bicistronic pre-mRNAs; and (b) authentic trans-splicing events between pre-mRNAs of distinct genes.