A 3.3kb fragment containing the 5' upstream region and 5' UTR of His3.3B is fused upstream of GFP. A fragment from the His3.3B 3' UTR containing the P1, P2 and P3 polyadenylation sites (nucleotides 3878-5666 according to GenBank accession X81207) is fused downstream of the GFP coding region.