Effects of the polyubiquitin gene Ubi.U4 leader intron and first ubiquitinmonomer on reporter gene expression in Nicotiana tabacum

We have previously shown by RNA gel blot analyses that the tobacco polyubiq uitin-encoding gene Ubi.U4 is expressed in a complex pattern during plant d evelopment (Genschik et al., 1994). In order to study its tissue-specific e xpression, we cloned the fragment containing the -263 bp proximal promoter of the gene, the leader intron and the first ubiquitin monomer in front of the reporter GUS gene. Histochemical analyses for GUS activity during tobac co plant development revealed that the gene is expressed at variable amount s in many plant tissues with high levels in metabolically active and/or div iding cells and in the vascular tissues of the plant. We also analysed the expression pattern of constructs in which either the intron or the intron t ogether with the first ubiquitin monomer were deleted. Our results indicate that the ubiquitin leader intron is not only a quantitative determinant of gene expression but may also influence the tissue-specific expression patt ern.