Hsp26 promoter region with a portion of the translated region (sequences from -1917 to +490 relative to the transcription start site). A 773bp SacI cDNA fragment derived from the barley SIP1 gene has been inserted at the 3' end to act as a marker that allows the transcript produced by this construct to be distinguished from endogenous Hsp26 transcripts. The Hsp70 termination sequence is present downstream of the SIP1 marker sequence.
Lines exhibiting position effect variegation (PEV) for the w+mW.hs allele of the P{hsp26-pt-T} construct show a reduction in heat shock expression compared to lines not showing PEV. Lines with the smallest amount of eye pigmentation show the lowest levels of heat induced Hsp26 expression, and the converse is true. The reduction in heat induced expression can be derepressed by Su(var)2052. Variegating transgenes show a reduction in accessibility to restriction enzyme digestion. This suggests that the chromatin packaging of an insert showing PEV is altered. Pericentric transgenes are packaged in a more regular array than euchromatic transgenes.