The non-coding transcripts of hsr-omega gene in Drosophila: Do they regulate trafficking and availability of nuclear RNA-processing factors?

The 93D or hsr-omega (hsr omega) is an unusual non-protein-coding gene with multiple transcription products which are dynamically expressed in most ce ll types of Drosophila melanogaster and this gene, besides being a member o f the heat shock gene family, is uniquely induced in polytene cells by a va riety of amides, The various aspects of this gene's organization, regulatio n and inducible properties are briefly reviewed. Recent data in our laborat ory show that absence of the hsr-omega transcripts because of nullosomy or over-expression of the these transcripts in specific cell types due to muta tion in the promoter region of this gene results in specific phenotypes. It is known from several earlier and our recent studies that in unstressed ce ll nuclei a variety of hnRNA binding proteins (hnRNPs) associate with many chromosomal sites, including the 93D, and with extrachromosomal speckles wh ere the hsr-omega transcripts also co-localize, Following heat shock and pr otein-coding products which other stresses, the bulk of these proteins and the hsr-omega nuclear (hsr omega-n) transcripts get localized to the 93D si te. We propose that one of the important functions of the hsr omega-n trans cripts is to act as a 'sink' for at least some members of the hnRNPs and re lated proteins so that any increase or decrease in the abundance of these n uclear transcripts correspondingly modifies the 'sink' size, which in turn affects the availability of such proteins in active nuclear compartments an d regulates the nuclear RNA processing activity; It appears that nonavailab ility or over-abundant availability of these transcripts disrupts the regul ated and fine-tuned balance of the various RNA-processing factors resulting in tuans-dominant mutant phenotypes. We believe that binding with specific proteins and consequent regulation of their activity may be a common featu re of the functions of non-protein coding genes.