The red blood cells (RBCs) of the chicken embryo are widely used to study late erythroid differentiation processes. The hypoxic mediators adenosine and norepinephrine (NE) stimulate the cAMP-depentend transcription of late erythroid genes like the well-known carbonic anhydrase II or other regulatory proteins like TOB or TIS7. Since the regulation of late erythroid maturation is not well established, we investigated the expression and localisation of TIS7.

Embryonic RBCs were incubated with NE and the expression of TIS7 protein expression over times was determined. In addition, we tested the effect of MG132, a proteasome inihibitor, on the stability of TIS7. Analysis of cytoplasmic extract containing TIS7 revealed that TIS7 is not a freely soluble protein but that it is completely associated with the polysomes, harbouring ribosomes, translation factors and erythroid mRNAs. The polysomes were futher analysed by centrifugation through a continuous sucrose gradient, supplied with EDTA which dissociates polysomes into small (40S) and large (60S) ribosomal subunits.

Under this conditions, TIS7 completely copurifies with the 40S ribosomal subunit. Although TIS7 has been mainly described as a transcriptional co-repressor, our datas suggest that TIS7 might regulate the translation of RBCs that express their latest erythroid genes.