Heat-shock inducible polyubiquitin gene UbI undergoes alternative initiation and alternative splicing in mature chicken testes.

Ubiquitin, a heat-shock protein highly expressed during spermatogenesis, plays an essential role in the differentiation of the germinal cells, particularly in the structural changes of chromatin taking place at the end of the process. To shed light on the mechanisms that modulate transcriptional activity of the heat-shock inducible polyubiquitin gene UbI during spermatogenesis and stabilize the message when transcription is not longer active, we have compared the characteristics of UbI transcripts in mature and immature testes and somatic cells. In mature chicken testes, transcription starts at a site placed closer to the heat-shock promoters than in somatic tissues. This site is upstream from the TATA box used in somatic cells. In addition, UbI transcript undergoes an alternative splicing that produces a longer 5' untranslated region in mature testis. These findings may provide a basis for the observed increase in expression of UbI in mature chicken testes and for the stability of the message when transcription ceases at the end of spermatogenesis.