Ubiquitin protein and regulation of heat shock genes

Ubiquitin protein and regulation of heat shock genes
A massive increase in the transcription of DNA sequences included in heat shock genes has been observed due to increase in temperature. Therefore, heat shock genes offer an ideal s-ystem for the study of regulation of gene activity. These genes occur in wide range of organisms ranging from bacteria to humans. It has been shown that a protein named ubiquitin plays a key role in this regulation.

The promoters of eukaryotic heat shock genes possess a response element called heat shock element (HSE) (Table 37.3) located upstream of these genes. The HSE is recognized by a 'heat shock transcription factor (HSTF)', which is active (perhaps through phosphorylation) only during heat shock and binds to a site (70bp) carrying HSE (15bp). About 20 genes carrying same HSE are switched on simultaneously, producing heat shock proteins. Both HSE and HSTF have been conserved during evolution. For instance, in yeast and fruitfly similar HSTF proteins and similar HSE (DNA sequences) have been found.

It is suggested that perhaps the heat shock transcription factor (HSTF) itself remains ubiquitinated under normal condition and that failure of ubiquitination renders this factor free to be available to attach to a sequence (HSE) meant to initiate transcription of heat shock genes. The role of ubiquitin in modification of nucleosome structure through its association with histone proteins has also been suggested.